Clarify user documentation around spam wave use of autoflagging permissions

[tripleee]

Just reiterating a discussion from Charcoal.

https://stackoverflow.com/c/charcoal/questions/868

In brief, update the documentation strings in metasmoke to clarify that opting in to autoflagging also means your flags will be eligible for use in spam waves, irrespective of your threshold settings etc for regular autoflagging.

[gparyani]

I highly agree with documenting this, given that some users have raised complaints about their flags being used in spam waves without anything pointing them to that fact.