Add README for ros-base.
Remove base image stuff and tweaks.

* Base image docs now in ros-base/README.md.
* Simplify ansible install section.
* Better examples.
Fix example.
Cleanup example.
Link ros-base
Fix heading
Fix bullets.
Add overall readme.
Add links to main sub projects.
Review: Add readme for ansible.
Merge branch 'F_readme_fixes' of github.com:shadow-robot/sr-build-tools into F_readme_fixes
Review: add sctructure section.
Merge pull request #91 from shadow-robot/F_readme_fixes

F readme fixes