Clarify whitelist strategy requirements

[josh-levinson]

RIght now it looks like to use the whitelist strategy, you have to:

1. Have a destination database
2. Destination database must already be created
3. Structure of tables and everything also has to be created
4. Data can't be in there, though?

I don't see any documentation of this anywhere, and I only figured it out by looking through past issues that matched problems I'd been having. It would be nice if the code examples or README explained this.