Update IRC network name in the README

KDE has moved from freenode to Libera Chat, update the README to reflect
this.

README.md

@@ -12,7 +12,7 @@ KWin is an easy to use, but flexible, composited Window Manager for Xorg windowi
 # Contacting KWin development team
 
  * mailing list: [kwin@kde.org](https://mail.kde.org/mailman/listinfo/kwin)
- * IRC: #kwin on freenode
+ * IRC: #kwin on irc.libera.chat
 
 # Support
 ## Application Developer
@@ -45,4 +45,4 @@ A new Feature can only be added to KWin if:
 
 All new added features are under probation, that is if any of the non-functional requirements as listed above do not hold true in the next two feature releases, the added feature will be removed again.
 
-The same non functional requirements hold true for any kind of plugins (effects, scripts, etc.). It is suggested to use scripted plugins and distribute them separately.
+The same non functional requirements hold true for any kind of plugins (effects, scripts, etc.). It is suggested to use scripted plugins and distribute them separately.