[Docs] Unlisting and centralizing the Contributing guide

[leecalcote]

Current State

https://docs.layer5.io/kanvas/reference/contributing-to-docs/ is displayed under Kanvas product docs.

Desired State

1. Ideally, this page is unlisted in the navbar, but is linked to from the footer and from CONTRIBUTING.md
2. Ideally, this page is moved to a generic location (not under a specific product)
3. Ideally, there are two contributing pages (or one page, but with the mechanics as secondary information):
   1. Writer's guide, inclusive of shortcodes and other resources specific to docs.layer5.io's framework.
   2. Mechanics of contributing (less important)

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Contributor Guide and Resources

• 📚 Instructions for contributing to documentation
  • Layer5 documentation site and source
• 🎨 Wireframes and designs for Layer5 site in Figma (open invite)
• 🙋🏾🙋🏼 Questions: Layer5 Discussion Forum and Layer5 Community Slack

[zihanKuang]

This issue is closed as it was resolved by #520