DOC: Update Non-Functional Twitter Link in `developer_guide.md` and rebrand twitter to X in `README.rst`..

[Demon-Sheriff]

Issue with current documentation:

- The current some critics Twitter link in the docs/source/contributing/developer_guide.md is no longer functional.

- Twitter link in README.rst should be updated to reflect the rebranding to X.

Idea or request for content:

Affected Files

• docs/source/contributing/developer_guide.md
• README.rst

Steps to Reproduce

1. Open the developer_guide.md file.
2. Click on the Twitter link to notice that it's not working.
3. Check the README.rst file to see the outdated Twitter link.

Expected Behavior

• The non-working Twitter link should be removed.
• The Twitter link should be updated to X in README.rst.

[welcome]

]
🎉 Welcome to PyMC! 🎉 We're really excited to have your input into the project! 💖

If you haven't done so already, please make sure you check out our Contributing Guidelines and Code of Conduct.

[Demon-Sheriff]

@twiecki @ricardoV94 Can you please take a look at PR #7451 for the issue.