put a note that error logs are only errors from Gunicorn.

fix #1124

Author: benoitc

docs/source/deploy.rst

@@ -267,6 +267,8 @@ utility::
 
 .. note:: overriding the LOGGING dictionary requires to set `disable_existing_loggers: False`` to not interfere with the Gunicorn logging.
 
+.. warning:: Gunicorn error log is here to log errors from Gunicorn, not from another application.
+
 .. _Nginx: http://www.nginx.org
 .. _Boom: https://github.com/rakyll/boom
 .. _`example configuration`: http://github.com/benoitc/gunicorn/blob/master/examples/nginx.conf