[Issue template] need to update/extend who to tag
This PR 

* [x] adds an entry for what to do what to do when someone has model hub issues - thank you, @julien-c!

TODO/Input needed:

* [ ] need to update who to tag for `tensorflow` Issues

@LysandreJik 

For broken models you would just tag the model author(s) – we'll add a feature to the model hub to tag someone in a conversation thread, but in the meantime you can use the Forum to ping them<|||||>That's a great idea to tag the model author - how would a user know the model author's corresponding forum username? I guess this is temporary so probably can be somehow figured out...<|||||>We use SSO so one's username on Forum is guaranteed to be one's username on hf.co<|||||>Ah, that's perfect then! Thank you!