Document release process.

Fixes #292.

This is mostly an initial sketch for discussion.

This also at least partially addresses #86, #87, #126, #277.
Looks like we still need to create a this spec file. Or maybe @tomprince has it locally?

```
$ rpmbuild --define="_sourcedir ${PWD}" --define="_rpmdir ${PWD}/results" -ba clusterhq-release.spec
error: failed to stat /home/richard/projects/HybridLogic/flocker/clusterhq-release.spec: No such file or directory
```