Fix error in reverse proxy example for how to include nginx override.

Also clarified where the file is included in the nginx configuration file.

docs/reverse.rst

@@ -244,7 +244,9 @@ Override Mailu configuration
 ----------------------------
 
 If you do not have the resources for running a separate reverse proxy, you could override Mailu reverse proxy configuration by using a Docker volume.
-Simply store your configuration file (Nginx format), in ``/mailu/nginx.conf`` for instance.
+Simply store your configuration file (Nginx format), in ``/mailu/overrides/nginx.conf`` for instance.
+All *.conf files will be included in the main server block of Mailu in nginx which listens on port 80/443.
+Add location blocks for any services that must be proxied.
 
 Then modify your ``docker-compose.yml`` file and change the ``front`` section to add a mount:
 
@@ -259,7 +261,7 @@ Then modify your ``docker-compose.yml`` file and change the ``front`` section to
       [...]
     volumes:
       - "$ROOT/certs:/certs"
-      - "$ROOT/nginx.conf:/etc/nginx/nginx.conf"
+      - "$ROOT/overrides/nginx:/overrides"
 
 You can also download the example configuration files: