Add link to Freenode (#9785)

README.md

@@ -65,6 +65,6 @@ Receive notifications of critical security updates. The sophistication of online
 - **Twitter** - Follow [Mattermost](https://twitter.com/mattermost)
 - **Blog** - Get the latest updates from the [Mattermost blog](https://about.mattermost.com/blog/).
 - **Email** - Subscribe to our [newsletter](http://mattermost.us11.list-manage.com/subscribe?u=6cdba22349ae374e188e7ab8e&id=2add1c8034) (1 or 2 per month)
-- **IRC** - Join us on #matterbridge (thanks to [matterircd](https://github.com/42wim/matterircd))
+- **IRC** - Join the #matterbridge channel on [Freenode](https://freenode.net/) (thanks to [matterircd](https://github.com/42wim/matterircd))
 
 Any other questions, mail us at info@mattermost.com. We’d love to meet you!