Help: Document ctest dashboard client usage

Extend the ctest(1) manual with a section describing configuration
and usage of CTest as a CDash software quality dashboard client.

Help/manual/cmake-commands.7.rst

@@ -128,6 +128,8 @@ versions of CMake.  Do not use them in new code.
    /command/variable_requires
    /command/write_file
 
+.. _`CTest Commands`:
+
 CTest Commands
 ==============