Add description of relay server variable for clarity

[tschettervictor]

Since the "rustdesk_hbbs_ip" is not where the server should listen on, but actually the relay server to use, I added a description that will clarify this

[paspo]

I think that variable rustdesk_hbbs_ip is misnamed: it is referring to a list of hbbr instances, so maybe it should be renamed to rustdesk_hbbr_list?

[rustdesk]

Yes

[tschettervictor]

Or perhaps “rustdesk_relay_servers” or something similar.

[rustdesk]

Agree

[tschettervictor]

Is it possible to set multiple relay servers using the -r option?