Clarify some metadata and update optional/required/recommended status.
Review Request #11732 — Created July 19, 2021 and submitted
This updates the definitions and examples for some of the metadata,
making it more clear how some are used and what values are expected.
Some of the required keys are now marked as recommended instead, since
it doesn't always make sense to include them. "Required" show now be
statsmetadata key is also now recommended, instead of merely
optional, as it's a very useful thing to include if available for
Built the docs. Read through the new changes. Checked the links for