Fix plugin updates.

README.md

@@ -314,7 +314,15 @@ and sign out at `https://<any-app>/_google-auth/logout`.
   stock nginx template.
 - **Plugin updates:** `sudo dokku plugin:update google-auth` rebuilds the
   service image and recreates the container with freshly written settings.
-  `dokku google-auth:report` names the running service's state; if it ever says
+  Editing the plugin directory in place works too: the image is tagged with a
+  fingerprint of its source, so `google-auth:restart` (and anything else that
+  starts the service) rebuilds when the Go code has moved rather than reusing
+  the binary that happens to be tagged. This matters because the shell half of
+  the plugin takes effect the moment the files change while the binary does
+  not, and a container running an older build accepts the mount, accepts
+  `GOOGLE_AUTH_APP_CONFIG_DIR`, and ignores both.
+  `dokku google-auth:report` names the running service's state — it asks the
+  service itself rather than trusting Docker's metadata — and if it ever says
   it is ignoring per-app lists, `dokku google-auth:restart` recreates it.
 - **An app's own lists need its nginx config to be current**, since that is
   what tells the service which app a request belongs to. The plugin rewrites