Simple:
# inside a jail!
$ wget <link to mdns.sh RAW from gist e.g https://gist.githubusercontent.com/Dakta/d37f038e90bcc68822efdc5b6d38985c/raw/36da05f072982e5836a03f0ca556f3c28a6cb1e2/mdns.sh>
$ chmod +x mdns.sh
$ ./mdns.sh
Use the original Gist if you want to execute this from outside a jail.