Update instructions for production deployment

docs/nginx_photos

@@ -43,7 +43,7 @@ server {
     }
 
     location / {
-        uwsgi_pass unix:///var/www/photos/photos21/photos21.sock;
+        uwsgi_pass unix:///var/run/uwsgi/app/uwsgi_photos/socket;
         include /etc/nginx/uwsgi_params;
     }
 }