docs: document automatic Postgres upgrades via pgautoupgrade

README.md

@@ -24,6 +24,14 @@
 5. `abra app deploy YOURAPPDOMAIN`
 6. Open the configured domain in your browser to finish set-up
 
+## Postgres upgrades
+
+The `db` service uses the
+[`pgautoupgrade`](https://github.com/pgautoupgrade/pgautoupgrade) image, so when
+the recipe bumps the Postgres major version the existing cluster is upgraded in
+place automatically on the next `deploy` — no manual migration steps. As with
+any major database upgrade, **take a backup of the `<stack_name>_db` volume
+first** (e.g. `abra app backup <domain>`).
+
 [`abra`]: https://git.coopcloud.tech/coop-cloud/abra
 [`coop-cloud/traefik`]: https://git.coopcloud.tech/coop-cloud/traefik
-p-cloud/traefik