Add precision about cmake cache
diff --git a/README.rst b/README.rst
index 43253be..6d18f54 100644
--- a/README.rst
+++ b/README.rst
@@ -77,6 +77,11 @@
cmake -D CMAKE_BUILD_TYPE:String="Debug" .
+Note that, with CMake, if you want to change the compiler or its options after you already ran CMake, you need to clear its cache first, eg (using GNU find)::
+
+ find . -iname '*cmake*' -not -name CMakeLists.txt -exec rm -rf {} +
+ CC=gcc CFLAGS='-fstack-protector-strong -Wa,--noexecstack' cmake .
+
In order to run the tests, enter::
make test
