docs(mail): correct module docstring re: maddy creds password subcmd

Follow-up to 6430945 — the module docstring still referenced the
wrong 'creds set' subcommand.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/mail/droplet.py

@@ -11,7 +11,8 @@ All commands are touchless / stateless / idempotent:
 * **Idempotent** — ``up`` adopts an existing droplet, never duplicates.
   DNS records are upserted (no error on existing). The smarthost block
   is fenced and replaced in place. Mailbox passwords use ``maddy creds
-  set`` first, then fall through to ``create``.
+  password`` first, then fall through to ``create`` + ``imap-acct create``
+  for first-time provision.
 """
 
 from __future__ import annotations