Document the release schedule and versioning system.
are > are to
Added to index
:ref: > :doc:
tickets > issues
which > who
Fix typo
bugfixes > bug fixes
American spelling
Pre-format instead of cite
Versioning > Version numbers
Address final review comments.
organizaion -> organization
Merge pull request #676 from ClusterHQ/release-schedule-versions-673

Document the release schedule and versioning system.