Update docs on CMake header-only usage

docs/source/build.rst

@@ -32,6 +32,22 @@ If you don't want to install **cglm** to your system's folder you can get static
   option(CGLM_USE_C99 "" OFF) # C11 
   option(CGLM_USE_TEST "Enable Tests" OFF) # for make check - make test
 
+**Use as header-only library with your CMake project example**
+This requires no building or installation of cglm.
+
+.. code-block:: CMake
+  :linenos:
+
+  cmake_minimum_required(VERSION 3.8.2)
+  
+  project(<Your Project Name>)
+  
+  add_executable(${PROJECT_NAME} src/main.c)
+  target_link_libraries(${LIBRARY_NAME} PRIVATE
+    cglm_headers)
+  
+  add_subdirectory(external/cglm/ EXCLUDE_FROM_ALL)
+
 **Use with your CMake project example**
 
 .. code-block:: CMake