Removed mkdocs based documentation.
Added skeleton of Sphinx docs.
Added doc contribution details.
Merge branch 'CPGFeedback' of https://github.com/NASA-Tensegrity-Robotics-Toolkit/NTRTsim into CPGFeedback
Merge branch 'CPGFeedback' of https://github.com/NASA-Tensegrity-Robotics-Toolkit/NTRTsim into CPGFeedback