Fix: About page has wrong copy for forum and Discord

[Shivrajsoni]

Fixes #3649

Changes:
Changes the Description of Discord , Code of Conduct ,Join the Forum Section
as mentioned in the issue

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test) 
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123
• meets the standards outlined in the accessibility guidelines

[welcome]

🎉 Thanks for opening this pull request! Please check out our contributing guidelines if you haven't already.

[release-com]

Release Environments

This Environment is provided by Release, learn more!
To see the status of the Environment click on Environment Status below.

• p5.js-web-editor
  • app-ted6137.release.editor.p5js.org/
  • preview-ted6137.release.editor.p5js.org/

🔧Environment Status : https://app.release.com/public/Processing%20Foundation/env-f1fc7438f1

[raclim]

Thanks so much for opening this PR—we really appreciate you taking the time to open this! At this time, we’re not able to accept it, since we generally ask contributors to be assigned to an issue before starting work. I’m sorry we couldn’t merge this one in, but we’d love for you to express interest in another issue!