Help/dev: Add a CMake Source Code Guide placeholder

Create a dedicated document to cover the CMake source code for
developers.

Help/dev/README.rst

@@ -29,3 +29,12 @@ following documents:
 .. _`CMake Repository`: https://gitlab.kitware.com/cmake/cmake
 .. _`CMake Review Process`: review.rst
 .. _`CMake Testing Process`: testing.rst
+
+Developer Documentation
+=======================
+
+CMake developer documentation is provided by the following documents:
+
+* The `CMake Source Code Guide`_.
+
+.. _`CMake Source Code Guide`: source.rst

Help/dev/source.rst

@@ -0,0 +1,7 @@
+CMake Source Code Guide
+***********************
+
+The following is a guide to the CMake source code for developers.
+See documentation on `CMake Development`_ for more information.
+
+.. _`CMake Development`: README.rst