Document strategy for storing database credentials

[jmcnevin]

Hello! Thanks for putting this gem together. It's been very helpful!

I'm wondering how you typically manage your database.yml config inside of the engine during a production deploy. Obviously, I don't want to get production database credentials checked into the gem's repo, and creating a new database.yml file inside of the engine during deployment could be a little tricky after the engine is gem-ified

I'm assuming that the only way to accomplish this would be make the config/database.yml inside of the engine almost entirely ERB-based, either passing in the credentials via ENV, or by reading a yml file in the hosting application.

This could be an important addition to this gem's README.

Thanks again.