Document what the purpose of the secondary config is vs primary.

[Billy]

Its not clear to me why the config has primary config and secondary. What's the purpose of that? Could you please document it?

[Lee Thomas]

Same for me, have asked a question here:

https://stackoverflow.com/questions/64693769/what-should-the-primary-and-secondary-ip-address-be-when-setting-up-stun-server