add FAQ for divergent changes

docs/FAQ.md

@@ -109,6 +109,17 @@ commit, then run `jj restore --from Y --to @-` to restore the parent commit
 to the old state, and `jj restore --from X` to restore the new working-copy
 commit to the new state.
 
+### What do I do with divergent changes?
+
+A divergent change (denoted by `??` after the change ID in the log) represents
+a change that has two or more visible commits associated with it. Most commonly,
+the way to resolve this is to abandon the unneeded commits.
+
+Usually, the different commits associated with the divergent change ID should all
+appear in the log, but due to #2476, they may not. If that happens, you can
+either use `jj log -r 'all()' | grep <change id>` or disable the
+`revsets.short-prefixes` config option.
+
 [config]: config.md
 
 [gitignore]: https://git-scm.com/docs/gitignore