README: Move wasp-os community chat to libera.chat

We also update the recommendation for those new to IRC to use
a matrix/IRC bridge instead of a simple IRC web client since that
should make the community a bit more interactive.

If you are curious about the move to libera.chat take a look at
the Linux Weekly News summary of the beginning of the end
(https://lwn.net/Articles/857140/ ) together with these
testimonials about the behaviour of the new freenode staff
which I think makes clear we have reached the end of the end:

 * https://nedbatchelder.com/blog/202106/goodbye_freenode.html
 * https://www.fsf.org/news/update-to-the-fsf-and-gnus-plan-to-move-irc-channels-to-libera.chat
 * https://twitter.com/irccloud/status/1404153550159159298

So... we're moving... and sorry for not making this decision sooner!

Signed-off-by: Daniel Thompson <daniel@redfelineninja.org.uk>

README.rst

@@ -73,12 +73,14 @@ Community
 The wasp-os community is centred around the
 `github project <https://github.com/daniel-thompson/wasp-os>`_ and is
 supplemented with instant messaging via the #wasp-os IRC channel at
-freenode.net.
+libera.chat .
 
-If you are unfamiliar with IRC we recommend the
-`offical freenode web client <https://webchat.freenode.net/#wasp-os>`_. Choose
-a nickname, leave *I have a password* unchecked, set the *Channel* to
-**#wasp-os** and click **Start**. That's it!
+If you are unfamiliar with IRC and don't have a preferred client then
+we recommend connecting to libera.chat using the
+`matrix/IRC bridge <https://app.element.io/#/room/#wasp-os:libera.chat>`_.
+The matrix bridge will allow us to receive messages whilst offline. Follow
+the link above and, if you do not already have a matrix account, register
+yourself. That should be enough to get you chatting!
 
 Videos
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