Commented "defaults" in overrides files

[jshufro]

It occurred to me a couple years late that there are some common patterns people like to add to the override yml. Trouble is, they don't know what they are, eg #682

We should catalogue some frequently used ones and add them to the blanks, but commented out, so users can just uncomment and adjust them.

This won't help with old installs, since the override files are untouched on upgrade, but at least new users will benefit.