Replace README with README.md (third draft)
Use https instead of http wherever supported by server.
README: module-specific user docs

linking to what the doc team wrote, yay!

/sbin -> /usr/sbin per http://en.opensuse.org/openSUSE:Usr_merge
README: module-specific developer docs -> doc/
Merge pull request #12 from yast/readme-draft-3

Replace README with README.md