[Docs] update `readme` and `contributing`

[nebula-aac]

Task: Update README.md and CONTRIBUTING

• [ ] Add some general information on how to get started with using this repo
• [ ] Update CONTRIBUTING document specifically to this repo workflow

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Contributor Guides and Resources

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