Update STK irc link to libera.chat

Author: Benau

README.md

@@ -3,7 +3,7 @@
 [![Apple build status](https://github.com/supertuxkart/stk-code/actions/workflows/apple.yml/badge.svg)](https://github.com/supertuxkart/stk-code/actions/workflows/apple.yml)
 [![Windows build status](https://github.com/supertuxkart/stk-code/actions/workflows/windows.yml/badge.svg)](https://github.com/supertuxkart/stk-code/actions/workflows/windows.yml)
 [![Switch build status](https://github.com/supertuxkart/stk-code/actions/workflows/switch.yml/badge.svg)](https://github.com/supertuxkart/stk-code/actions/workflows/switch.yml)
-[![#supertuxkart on the freenode IRC network](https://img.shields.io/badge/freenode-%23supertuxkart-brightgreen.svg)](https://webchat.freenode.net/?channels=supertuxkart)
+[![#supertuxkart on the libera IRC network](https://img.shields.io/badge/libera-%23supertuxkart-brightgreen.svg)](https://web.libera.chat/?channels=#supertuxkart)
 
 SuperTuxKart is a free kart racing game. It focuses on fun and not on realistic kart physics. Instructions can be found on the in-game help page.