FAQ appendix cleanup

[rhiaro]

For #728

Removed FAQ style headings and responses, trimmed down some text, made some language consistent.

Note - one subsection said DID docs can be used to serve representations of resources, like schemas. I thought the group had resolved that DID docs should have minimal stuff for the specific needs of DIDs, and that any more than this was bad practice (per the resource=true discussion) so I've updated it to say to use a DID parameter to do this but didn't mention the resource parameter as it still doesn't have a spec linked in the Registries. This is a separate commit though so can revert if I got the wrong end of the stick.

Also added a paragraph aiming to address #718 about whether the DID subject can change.

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Preview | Diff

[iherman]

Thanks @rhiaro,

• I do not think the (new) title "Implementation Guidance" is an appropriate replacement for FAQ. Many (most?) of the sections are related to the way DID are to be used rather than implemented, and they also often clarify conceptual details. I am not sure what to offer instead, though. "Usage Notes", "Usage Guidance"...: neither of these sound exactly right, but I am sure you can come up with something better.
• Several sections make use of the alsoKnownAs property but the property itself is still marked as at risk. I seem to remember that, after all, alsoKnownAs will stay as a bona-fide property, but I did not see any PR or issue on this. It would be good to sync this...
• This is a more general editorial issue, in fact. I think it is good practice to mark all appendices (maybe except for the IANA one) as non-normative.
  Another approach would be to put a generic statement into the conformance section. But I personally think marking each appendix as non-normative is better.

[rhiaro]

Thanks @iherman. I meant to note about the main heading - I definitely wasn't sure about Implementation Guidance, and was looking for feedback on that.

I thought appendices were non-normative by definition, but I can add that explicitly if necessary.

If alsoKnownAs gets dropped during CR we can certainly remove mentions of it from the appendices.

[brentzundel]

Perhaps this could be

Suggested change

	<h1>Implementation Guidance</h1>
	<h1>Appendix</h1>

[msporny]

We have multiple appendices... If we took this change, the spec would read: "Appendix C: Appendix"... which might not be the most helpful title. :P

[msporny]

Editorial, multiple positive reviews, no objections, merging.