Release Documentation

[mnorton]

I just added a pull request to add the get-sakai file. Currently, it links to the binary and source installation instructions for 2.9. The issue concerns release documentation. Will we continue to put release notes into Confluence? If the intent is to move future release notes and instructions to this repo, then I think we should start by migrating the current 2.9 documentation. This will give us a chance to see how we might break it up, etc. We should give consideration to marking certain pages with a release number, as is done in the Moodle documentation.