docs: where ipx keeps the directory's token, and replacing it (#205)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/directory.md

@@ -16,6 +16,11 @@ this server, and whether to share. ipx asks the directory on its people's behalf
 talks to it and never sees the token or a feed's address. With no directory set up, the Directory
 says so and feeds are added by their address.
 
+ipx keeps the address and token with its other server settings, in its database (`settings`,
+`directory_url` and `directory_token`), not in config.toml. The token is written, never shown
+again: the tab says it is set and offers to clear it. To replace one, make a new token on the
+directory, paste it over the old, then delete the old token's entry from the directory's config.
+
 With sharing on, ipx sends its snapshot after every scan, whenever the catalogue or these settings
 change, and every half hour: each feed checked at least once, with how many people here subscribe,
 and the category an admin gave a feed that names none. It never sends an OPML or a Patreon creator