Ahodges/documenttion/doc387

@sarina @carsongee, please review for accuracy.
@mhoeber , @srpearce , please copy edit and proofread.
@WatsonEmily , for distribution to PMs for feedback as needed.
An image of the new options on the Staff Debug viewer is available in thi sPR for reference: https://github.com/edx/edx-platform/pull/2686