Refactor README.md.
Move the original README.md to src since it's talking about C++
exclusively and add a more general README.md to document how
to install protoc for all languages.
diff --git a/src/README.md b/src/README.md
new file mode 100644
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--- /dev/null
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@@ -0,0 +1,209 @@
+Protocol Buffers - Google's data interchange format
+===================================================
+
+[](https://travis-ci.org/google/protobuf) [](https://ci.appveyor.com/project/protobuf/protobuf)
+
+Copyright 2008 Google Inc.
+
+https://developers.google.com/protocol-buffers/
+
+C++ Installation - Unix
+-----------------------
+
+To build protobuf from source, the following tools are needed:
+
+ * autoconf
+ * automake
+ * libtool
+ * curl (used to download gmock)
+
+On Ubuntu, you can install them with:
+
+ $ sudo apt-get install autoconf automake libtool curl
+
+On other platforms, please use the corresponding package managing tool to
+install them before proceeding.
+
+If you get the source from github, you need to generate the configure script
+first:
+
+ $ ./autogen.sh
+
+This will download gmock source (which is used for C++ Protocol Buffer
+unit-tests) to the current directory and run automake, autoconf, etc.
+to generate the configure script and various template makefiles.
+
+You can skip this step if you are using a release package (which already
+contains gmock and the configure script).
+
+To build and install the C++ Protocol Buffer runtime and the Protocol
+Buffer compiler (protoc) execute the following:
+
+ $ ./configure
+ $ make
+ $ make check
+ $ sudo make install
+ $ sudo ldconfig # refresh shared library cache.
+
+If "make check" fails, you can still install, but it is likely that
+some features of this library will not work correctly on your system.
+Proceed at your own risk.
+
+For advanced usage information on configure and make, please refer to the
+autoconf documentation:
+
+ http://www.gnu.org/software/autoconf/manual/autoconf.html#Running-configure-Scripts
+
+**Hint on install location**
+
+ By default, the package will be installed to /usr/local. However,
+ on many platforms, /usr/local/lib is not part of LD_LIBRARY_PATH.
+ You can add it, but it may be easier to just install to /usr
+ instead. To do this, invoke configure as follows:
+
+ ./configure --prefix=/usr
+
+ If you already built the package with a different prefix, make sure
+ to run "make clean" before building again.
+
+**Compiling dependent packages**
+
+ To compile a package that uses Protocol Buffers, you need to pass
+ various flags to your compiler and linker. As of version 2.2.0,
+ Protocol Buffers integrates with pkg-config to manage this. If you
+ have pkg-config installed, then you can invoke it to get a list of
+ flags like so:
+
+ pkg-config --cflags protobuf # print compiler flags
+ pkg-config --libs protobuf # print linker flags
+ pkg-config --cflags --libs protobuf # print both
+
+ For example:
+
+ c++ my_program.cc my_proto.pb.cc `pkg-config --cflags --libs protobuf`
+
+ Note that packages written prior to the 2.2.0 release of Protocol
+ Buffers may not yet integrate with pkg-config to get flags, and may
+ not pass the correct set of flags to correctly link against
+ libprotobuf. If the package in question uses autoconf, you can
+ often fix the problem by invoking its configure script like:
+
+ configure CXXFLAGS="$(pkg-config --cflags protobuf)" \
+ LIBS="$(pkg-config --libs protobuf)"
+
+ This will force it to use the correct flags.
+
+ If you are writing an autoconf-based package that uses Protocol
+ Buffers, you should probably use the PKG_CHECK_MODULES macro in your
+ configure script like:
+
+ PKG_CHECK_MODULES([protobuf], [protobuf])
+
+ See the pkg-config man page for more info.
+
+ If you only want protobuf-lite, substitute "protobuf-lite" in place
+ of "protobuf" in these examples.
+
+**Note for Mac users**
+
+ For a Mac system, Unix tools are not available by default. You will first need
+ to install Xcode from the Mac AppStore and then run the following command from
+ a terminal:
+
+ $ sudo xcode-select --install
+
+ To install Unix tools, you can install "port" following the instructions at
+ https://www.macports.org . This will reside in /opt/local/bin/port for most
+ Mac installations.
+
+ $ sudo /opt/local/bin/port install autoconf automake libtool
+
+ Then follow the Unix instructions above.
+
+**Note for cross-compiling**
+
+ The makefiles normally invoke the protoc executable that they just
+ built in order to build tests. When cross-compiling, the protoc
+ executable may not be executable on the host machine. In this case,
+ you must build a copy of protoc for the host machine first, then use
+ the --with-protoc option to tell configure to use it instead. For
+ example:
+
+ ./configure --with-protoc=protoc
+
+ This will use the installed protoc (found in your $PATH) instead of
+ trying to execute the one built during the build process. You can
+ also use an executable that hasn't been installed. For example, if
+ you built the protobuf package for your host machine in ../host,
+ you might do:
+
+ ./configure --with-protoc=../host/src/protoc
+
+ Either way, you must make sure that the protoc executable you use
+ has the same version as the protobuf source code you are trying to
+ use it with.
+
+**Note for Solaris users**
+
+ Solaris 10 x86 has a bug that will make linking fail, complaining
+ about libstdc++.la being invalid. We have included a work-around
+ in this package. To use the work-around, run configure as follows:
+
+ ./configure LDFLAGS=-L$PWD/src/solaris
+
+ See src/solaris/libstdc++.la for more info on this bug.
+
+**Note for HP C++ Tru64 users**
+
+ To compile invoke configure as follows:
+
+ ./configure CXXFLAGS="-O -std ansi -ieee -D__USE_STD_IOSTREAM"
+
+ Also, you will need to use gmake instead of make.
+
+**Note for AIX users**
+
+ Compile using the IBM xlC C++ compiler as follows:
+
+ ./configure CXX=xlC
+
+ Also, you will need to use GNU `make` (`gmake`) instead of AIX `make`.
+
+C++ Installation - Windows
+--------------------------
+
+If you only need the protoc binary, you can download it from the release
+page:
+
+ https://github.com/google/protobuf/releases
+
+In the downloads section, download the zip file protoc-$VERSION-win32.zip.
+It contains the protoc binary as well as public proto files of protobuf
+library.
+
+To build from source using Microsoft Visual C++, see cmake/README.md.
+
+To build from source using Cygwin or MinGW, follow the Unix installation
+instructions, above.
+
+Binary Compatibility Warning
+----------------------------
+
+Due to the nature of C++, it is unlikely that any two versions of the
+Protocol Buffers C++ runtime libraries will have compatible ABIs.
+That is, if you linked an executable against an older version of
+libprotobuf, it is unlikely to work with a newer version without
+re-compiling. This problem, when it occurs, will normally be detected
+immediately on startup of your app. Still, you may want to consider
+using static linkage. You can configure this package to install
+static libraries only using:
+
+ ./configure --disable-shared
+
+Usage
+-----
+
+The complete documentation for Protocol Buffers is available via the
+web at:
+
+ https://developers.google.com/protocol-buffers/
