Wave 12 updates, survey outages, etc.

[capnrefsmmat]

Several updates to the survey documentation.

Prerequisites:

• Unless it is a documentation hotfix it should be merged against the dev branch
• Branch is up-to-date with the branch to be merged with, i.e. dev
• Build is successful
• Code is cleaned up and formatted

Summary

• Document the released version of Wave 12
• Document how race/ethnicity items are coded
• Mention temporary sampling outage
• Don't point to OUTAGES.txt, since we don't use it

[krivard]

Wichada approved through Slack