Document RTFD hook job template in StackForge doc

* doc/source/stackforge.rst: Add basic documentation for the RTFD
job template. Also remove references to pylint and pyflakes jobs
which are mostly phased out due to increased flake8 popularity.

Change-Id: I0a1461a6c766a85cfac49ffed1b44358aabb2bc1
Merge "Document RTFD hook job template in StackForge doc"