Add documentation on how to use in various systems

[blakeembrey]

For example, combining with Heroku and https://devcenter.heroku.com/articles/preboot. This is more important once I merge database plugin support with locking and data/schema migration separation.

Basically, you can use preboot-like behaviour to achieve zero downtime through:

• Run schema migrations during reboot of an application (no preboot)
• When there's no schema migrations, you should enable preboot
• Run data migrations as a separated script (maybe two new fields in migrations scripts like dataUp and dataDown, poststart and postdown, etc - open to suggestions)

[ianstormtaylor]

This would be really awesome, a lot of people would find it useful.