Fixes #6929

Changes:

• Updated the contributor docs link in CONTRIBUTING.md to point to the correct page: https://p5js.org/contribute/.
• Updated the community statement link to point to the correct section on the website: https://p5js.org/about/#community-statement.
• Added a link to the Discord server alongside the forum link, mentioning the #contribute-to-p5 channel as suggested in the issue.

These changes address the outdated links identified in issue #6929, making the contribution guide more accurate and helpful for new contributors.

Screenshots of the change:

N/A (Text-only change in Markdown file)

PR Checklist

• npm run lint passes (Make sure to run npm run lint locally. If it passes, check this box [x])
• Inline reference update N/A (This PR modifies a documentation file, not library code with inline reference comments)
• Unit tests update N/A (This PR modifies a documentation file, no unit tests required)

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Thank You!

Thanks for spotting the issue and addressing it, @RishiAhuja ! I'll merge this shortly. In the future, please ask to be assigned on the issue before filing the PR, especially in more complex cases where technical consensus is needed before work can go ahead (the "Introduction" section of the contributor guideline has a bit more about this).

Thanks for merging, @ksen0, I appreciate it! And thanks for the feedback regarding assignment. My thinking was that since the issue was inactive for a while after your comment detailing the exact link updates needed, and it was a straightforward documentation change. But I understand the importance of signaling intent first, especially for coordination on bigger tasks. I'll be sure to comment and ask to be assigned next time before starting work. Looking forward to contributing more!