Added Release Notes

Release notes for v.1.1 have been added to the docs index.md page. Made some revisions to
other content to make it shorter.

Docker-DCO-1.1-Signed-off-by: Fred Lifton <fred.lifton@docker.com> (github: fredlf)
Corrected version number to 3 digits.

Docker-DCO-1.1-Signed-off-by: Fred Lifton <fred.lifton@docker.com> (github: fredlf)
Merge pull request #6824 from fredlf/1-1_release_notes

Added Release Notes