[doc] Properly document CMake minimum required version as 3.13 (#2162)

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 254fd37..ae02e77 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,4 +1,4 @@
-# Require CMake 3.10. If available, use the policies up to CMake 3.22.
+# Require CMake 3.13. If available, use the policies up to CMake 3.22.
 cmake_minimum_required (VERSION 3.13...3.22)
 
 project (benchmark VERSION 1.9.5 LANGUAGES CXX)

README.md

diff --git a/README.md b/README.md
index db99409..ab08e1f 100644
--- a/README.md
+++ b/README.md
@@ -77,9 +77,7 @@
 # Make a build directory to place the build output.
 $ cmake -E make_directory "build"
 # Generate build system files with cmake, and download any dependencies.
-$ cmake -E chdir "build" cmake -DBENCHMARK_DOWNLOAD_DEPENDENCIES=on -DCMAKE_BUILD_TYPE=Release ../
-# or, starting with CMake 3.13, use a simpler form:
-# cmake -DBENCHMARK_DOWNLOAD_DEPENDENCIES=on -DCMAKE_BUILD_TYPE=Release -S . -B "build"
+$ cmake -DBENCHMARK_DOWNLOAD_DEPENDENCIES=on -DCMAKE_BUILD_TYPE=Release -S . -B "build"
 # Build the library.
 $ cmake --build "build" --config Release
 ```

docs/dependencies.md

diff --git a/docs/dependencies.md b/docs/dependencies.md
index 98ce996..fdb7f19 100644
--- a/docs/dependencies.md
+++ b/docs/dependencies.md
@@ -5,7 +5,7 @@
 
 ## CMake
 
-The current supported version is CMake 3.10 as of 2023-08-10. Most modern
+The current supported version is CMake 3.13 as of 2024-10-24. Most modern
 distributions include newer versions, for example:
 
 * Ubuntu 20.04 provides CMake 3.16.3