Update social links

[jefftriplett]

A common complaint in our circles is that Twitter's demised has hurt our marketing attempts. I think we should:

• Add Mastodon?
• Add Bluesky?
• Rename Twitter to X

[glasnt]

I would be supportive of adding a number of optional social media links to event files. The template should optionally show "Follow on (platform)" if that value exists for the event. (Perhaps this should be "Follow on: X, Mastodon" etc

I would also support changing Twitter to "Follow on Twitter/X" (Or just "Follow on X").