* README.md: Improve IRC part

Use Libera Chats own webchat, list the website instead of the irc server pool

* en.motd: Point to the website instead of the irc server pool

* de.motd: Point to the website instead of the irc server pool

* ru.motd: Point to the website instead of the irc server pool

* zh_CN.motd: Point to the website instead of the irc server pool