Moved from Freenode to Libera.Chat

I created #btrbk channel on irc.libera.chat, and will observe the situation with freenode. I will still be present on irc.freenode.net, as long as the situation allows it.

The official IRC channel for btrbk will be moved to irc.libera.chat soon, we apoligize for the inconvenience.

Why?

[Libera.chat](https://libera.chat) promises independence and a free place to discuss open source projects, which sounds promising and worth to support:

> Libera.Chat aims to be a place where free / libre / open source software projects, peer directed projects, and their communities can communicate, collaborate, and flourish. In order to be a welcoming place for everyone and as required by Swedish law, there are some base rules that are valid for the entire network.

https://libera.chat/policies