docs: replace Gitter w/ Zulip and Twitter w/ Bluesky

[batpigandme]

Resolves # .

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Description

What is the purpose of this pull request?

This pull request replaces Gitter with Zulip for chat, and Twitter with Bluesky for contact.

Related Issues

Does this pull request have any related issues?

No

Questions

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No.

Other

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No.

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@stdlib-js/reviewers

[kgryte]

LGTM. Thanks, @batpigandme!

[kgryte]

I'll go ahead and merge, as we will still need to deploy the site for these changes to go live.