Add an include in cmake.rst
diff --git a/docs/cmake.rst b/docs/cmake.rst
index 41f58ff..5952920 100644
--- a/docs/cmake.rst
+++ b/docs/cmake.rst
@@ -15,6 +15,8 @@
# Add a CMake parameter for choosing a desired Python version
set(EXAMPLE_PYTHON_VERSION "" CACHE STRING "Python version to use for compiling the example library")
+
+ include(CheckCXXCompilerFlag)
# Set a default build configuration if none is specified. 'MinSizeRel' produces the smallest binaries
if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)