Add a comment to this Jira issue with the FAQ entry (both the question and the answer) you would like to be added to
http://db.apache.org/derby/faq.html, and the assignee will add it. Setting the "Patch Available" flag is a great way to keep a new FAQ on the radar until committed, even if the text of the FAQ is in a comment instead of in an actual patch.
Indicate in your comment if the FAQ belongs in the "Developing Derby" or "Using Derby" section.