Community page points to old site on PyMCon; let's point to new site

[reshamas]

On this page:
https://www.pymc.io/community/index.html

1. need to point to new PyMCon site:
   https://pymcon.com/

2. Let's include the hashtag here.

current

The PyMC community organizes PyMCon, whose last edition was in 2020. Follow Discourse or Twitter to be updated about the next edition!

change to:

The PyMC community organizes PyMCon, whose last edition was in 2020. Follow us on any or all platforms for updates: Discourse, LinkedIn, YouTube and Twitter. Our official hashtag is #pymcon.

[OriolAbril]

We should also update the announcement cards: https://www.pymc.io/welcome.html#announcements. cc @canyon289 @cuchoi @cluhmann

[cluhmann]

Good to close?

[OriolAbril]

The announcements in the landing page need to be updated too

[reshamas]

@cluhmann @OriolAbril
Closing this issue and opened a new one, #64
Information in comments for additional work (such as here) means it might be missed and it's easier to see the changes needed in a new issue.

It's also less daunting for new contributors who are submitting a simple PR, and we can avoid compounding their work. For new contributors, it is rewarding to be able to submit some small PRs.