Framework: Add Wiki entry to describe useful email filters to help with github spam

Created by: william76

@trilinos/framework

A conversation came up today in our meeting with @bartlettroscoe about the email spam being sent out by github, especially since we started using the PR tester, which adds a few comments to every PR, which generates an email each time. We thought a wiki article for Trilinos would be useful to go over useful email filter settings to help cut down the spam.

Generally speaking, I think what many people do is they filter out all the spam unless there is an @mention to them or a team they're on... but I think many people don't do this. So an article we can point people to would be useful.

This relates to some old issues #1674 #668 (closed)