Add feature_request mechanism

This will be standart way for end users to ask Rally team to get
some new feature.

The idea is to make it realy simple for end users to ask about covering
their use cases.

E.g. to add request users don't need to deep dive in rally community,
road map and how it works. They need just to share their use cases
that is not covered by current rally functionality.

As a bonus adding some Readme.rst files related to doc/* dirs

Change-Id: I4c615101012ac9d1668ed766ac831f7e5c8129a8
Merge "Add feature_request mechanism"