fix: remove references to x, correct community

[turnrye]

• Remove references to x.com since that's not actively being used for news posts
• Add reference to mastodon on get in touch since that is being used
• Clarify that community chats are on both Discord and Matrix
• Clarify that the community chat bridge isn't guaranteed, and that Discord has more activity

Fixes #65

[TessHull]

you've left the strong encouragement to use matrix in place; that feels like a dangerous new-user-experience decision since some people are going to follow that advice and end up in a dead end.
other than that, it looks like a good improvement

[silseva]

x.com is still being used, we post both there and on mastodon. However, for some obscure reason (and there is a lot of other people in the same situation), the posts are not visible unless you are logged in or you use a tool like nitter.