Change IRC channel to LiberaChat in README (#16279)
Change IRC channel to LiberaChat in README (#16279)

Freenode was taken over by a different entity, and former Freenode
staff created LiberaChat.

Short summary of the situation: https://blog.bofh.it/debian/id_461

With more details:

* https://gist.github.com/joepie91/df80d8d36cd9d1bde46ba018af497409
* https://gist.github.com/aaronmdjones/1a9a93ded5b7d162c3f58bdd66b8f491
MitarashiDango/mastodon,theoria24/mastodon,tootcafe/mastodon,MitarashiDango/mastodon,lindwurm/mastodon,cobodo/mastodon,koba-lab/mastodon,h3zjp/mastodon,yukimochi/mastodon,tootsuite/mastodon,maa123/mastodon,pinfort/mastodon,Kirishima21/mastodon,maa123/mastodon,musashino205/mastodon,tootcafe/mastodon,tootsuite/mastodon,pinfort/mastodon,pinfort/mastodon,glitch-soc/mastodon,ykzts/mastodon,tootsuite/mastodon,MitarashiDango/mastodon,Kirishima21/mastodon,glitch-soc/mastodon,masto-donte-com-br/mastodon,abcang/mastodon,imas/mastodon,abcang/mastodon,koba-lab/mastodon,im-in-space/mastodon,Ryanaka/mastodon,ykzts/mastodon,im-in-space/mastodon,cobodo/mastodon,tootsuite/mastodon,gol-cha/mastodon,primenumber/mastodon,h3zjp/mastodon,maa123/mastodon,primenumber/mastodon,ikuradon/mastodon,masto-donte-com-br/mastodon,theoria24/mastodon,maa123/mastodon,musashino205/mastodon,koba-lab/mastodon,gol-cha/mastodon,Ryanaka/mastodon,yukimochi/mastodon,tootcafe/mastodon,abcang/mastodon,im-in-space/mastodon,imas/mastodon,musashino205/mastodon,lindwurm/mastodon,imas/mastodon,yukimochi/mastodon,theoria24/mastodon,tootcafe/mastodon,masto-donte-com-br/mastodon,primenumber/mastodon,yi0713/mastodon,gol-cha/mastodon,glitch-soc/mastodon,masto-donte-com-br/mastodon,Ryanaka/mastodon,abcang/mastodon,cobodo/mastodon,imas/mastodon,cobodo/mastodon,ykzts/mastodon,Kirishima21/mastodon,Kirishima21/mastodon,yi0713/mastodon,ykzts/mastodon,gol-cha/mastodon,ikuradon/mastodon,MitarashiDango/mastodon,pinfort/mastodon,theoria24/mastodon,Ryanaka/mastodon,musashino205/mastodon,koba-lab/mastodon,glitch-soc/mastodon,h3zjp/mastodon,h3zjp/mastodon,yi0713/mastodon,primenumber/mastodon,yi0713/mastodon,yukimochi/mastodon,lindwurm/mastodon,ikuradon/mastodon,ikuradon/mastodon,lindwurm/mastodon,im-in-space/mastodon