Add user documentation for event names and synonyms

[lpsinger]

Description

Add documentation text and in-page help (as appropriate) to explain event names, event grouping, and how to request a group association, to end-users.

Acceptance criteria

• Identify a place for the documentation: an existing page, or a new page. Please propose that location for feedback before starting writing.
• Identify places in the UI where inline help, title/hover text, paragraphs of explanation, etc. are helpful.
• Explain the following:
  • How do you search by event name vs. full text?
  • How are event names determined? How are event names associated with each other?
  • How do you request changes to event names or group membership?
  • How do you bookmark an event or group?

[jracusin]

Identify a place for the documentation: an existing page, or a new page. Please propose that location for feedback before starting writing.

• We make a new docs page in /docs/circulars/eventid, where we describe the topics in the acceptance criteria.
• We also add a section on /docs/circulars/archive for eventid, linking to the new eventid page.

[lpsinger]

Hmm, how about just adding text to these pages:

• https://gcn.nasa.gov/docs/circulars/archive
• https://gcn.nasa.gov/docs/circulars/corrections
• https://gcn.nasa.gov/news