Hi Juliusz

1. I could easily add an option to Galène to restrict the range of
  ephemeral ports used — for example, you could set the range of ports to
  50000-60000, and only these ports would need to be forwarded.  Let me
  know if you think this is useful.

It might be useful to make possible the use of 2 distincts coturn servers 

In my case I would like one for nextcloud and one for Galène.

Nextcloud uses the use-auth-secret

Authentification and it turns out that I was unable to use it with Galene, event setting "credentialType": "hmac-sha1 » as described in your README file.

2. If you're using the built-in TURN server behind NAT (not recommended),
  you need to set up hairpinning in your NAT.  I don't see any good way
  around it.  Please mention it in the README.

The installation script  do not the use the built-in  turn but install and configure coturn. Galene is launched with the « -turn auto » option. 

Would you like me to add this information ?

Thanks again,

I am very pleased to contribute to the collective effort.

Fabrice.