+public-inbox-extindex does not currently write to the
+L<public-inbox-config(5)> file, configuration may be entered
+manually. The extindex name of C<all> is a special case which
+corresponds to indexing C<--all> inboxes. An example for
+C<--all> is as follows:
+
+ [extindex "all"]
+ topdir = /path/to/extindex_dir
+ url = all
+ coderepo = foo
+ coderepo = bar
+
+See L<public-inbox-config(5)> for more details.