Add note for NginX when running OC in subdir

admin_manual/installation/nginx_configuration.rst

@@ -9,6 +9,10 @@ Nginx Configuration
 -  Make sure your SSL certificates are readable by the server (see `Nginx HTTP 
    SSL Module documentation <http://wiki.nginx.org/HttpSslModule>`_).
 
+.. note:: The following example assumes that your ownCloud is installed in
+   your webroot. If you're using a subfolder you need to adjust the configuration
+   accordingly.
+
 .. code-block:: python
 
   upstream php-handler {