Use the sso marker

POSTINSTALL.md

@@ -1,10 +1,11 @@
-This app integrates optionally with Cloudron SSO.
+Use the following credentials:
 
-When using Cloudron SSO, Cloudron adminstrators are automatically made WordPress
-administrators. Non-administrators get the `editor` role by default.
+username: `admin`
 
-When _not_ using Cloudron SSO, the `admin` password is `changeme`.
+password: `changeme`
 
-You can access the dashboard directly at `/wp-admin/` (trailing slash is
-important!).
+=== sso ===
+
+Cloudron adminstrators are automatically made WordPress administrators.
+Non-administrators get the `editor` role by default.