Hi Brant,
This depends on who the audience is. Do you have one, or many administrators? Is this to communicate to a wider team (administrators in different geographic locations), or is it a note to your future self?
You can go for simple solutions by leaving notes in the custom field - tip, wrap it in <!-- -->, and then it appears to admins, but does not appear to end users on any screen.
The middle ground solution is to collaborate on a table/page in Confluence. This has the advantage of a revision history.
More complex solutions include marketplace apps such as https://marketplace.atlassian.com/apps/1219628/glass-project-documentation-for-jira?hosting=server&tab=overview
Consider too how new fields are added. Do they go through an approval process? If so, having a Jira project for this purpose, with one issue per custom field, to track approvals, add comments, track status ("backlog", "awaiting approval", "testing", "in uat", "Live"), may be a solution for you.
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