CouchApp database should exist outside the container

[terinjokes]

The CouchApp database that backs npmjs should exist outside the container, to allow for easy upgrades of the container without losing the entire database.

[nathanleiby]

@terinjokes thanks for sharing this great project. have you made any progress toward implementing this improvement?

[terinjokes]

I've started working on it, but running into issues around when the DB is available. Will probably just become a documentation thing.