Document release process.

Fixes #292.

This is mostly an initial sketch for discussion.

This also at least partially addresses #86, #87, #126, #277.
I tried creating a `0.0.2pre1` version, but the rpm builder failed with 
```
python-flocker.src: E: invalid-version 0.0.2pre1
python-flocker.noarch: E: invalid-version 0.0.2pre1
flocker-cli.noarch: E: invalid-version 0.0.2pre1
flocker-node.noarch: E: invalid-version 0.0.2pre1
```