Prepare for release

* Update Rakefile from https://github.com/talk-to/Chocolate
* Add release checklist to README.
Wrong grammar. Should be
```
* Publish, via `rake publish`. This will:
```

I'll fix the original in Chocolate master.

In fact, I'm thinking I'll just remove the explanation of what `rake publish` does and just mention
```
* Commit your changes.

* `rake publish`.
```