Add original comments to included nginx configuration.

Author: Matthias Erll

contrib/nginx/docker-registry.conf

@@ -1,5 +1,5 @@
 proxy_pass                       http://docker-registry;
-proxy_set_header  Host           $http_host;
-proxy_set_header  X-Real-IP      $remote_addr;
-proxy_set_header  Authorization  "";
+proxy_set_header  Host           $http_host;   # required for docker client's sake
+proxy_set_header  X-Real-IP      $remote_addr; # pass on real client's IP
+proxy_set_header  Authorization  ""; # see https://github.com/dotcloud/docker-registry/issues/170
 proxy_read_timeout               900;