Add homebrew guidelines to release checklist or automate PR generation

[laserson]

I think we have a few issues re: updating the homebrew version.

[heuermh]

I've been doing this manually and haven't run into any problems other than sometimes the release version will build and the HEAD will fail, but I suppose that's the nature of a HEAD build. Do you have any specifics in mind?

[laserson]

Does this reflect our current release process?

https://github.com/bigdatagenomics/adam/tree/master/scripts/release

If so, we should add a note to also update homebrew

[fnothaft]

That's pretty close, yeah.

[heuermh]

The release README could use an update with this, link fix (--> http://central.sonatype.org/pages/releasing-the-deployment.html#close-and-drop-or-release-your-staging-repository), and also #936