This commit changes the official Quassel IRC channel, (#quassel)

This commit changes the official Quassel IRC channel, (#quassel)
from the Freenode IRC network to the Libera IRC network in response
to recent issues which resulted in the entire volunteer staff of
Freenode stepping down.

For more information about this situation, please read this:
https://gist.github.com/joepie91/df80d8d36cd9d1bde46ba018af497409