Bring subheadings more in tune with expected CTRT standards.
Rename subheadings to use present tense instead of gerunds.
Clean up a lot of gunky old wording.

As part of this work, I realized an important part of the forking
instructions were captured on a more generic advanced-settings page.
I've pulled that information back into this page, where it belongs.
That page also had some forking-related troubleshooting info that
also should have been here. I reunited that troubleshooting info
here as well.