site: Update NSM state on CNCF landscape

[NikitaSkrynnik]

Description

We should fix all issues listed here: https://clomonitor.io/projects/cncf/network-service-mesh

Decomposition

Documentation

• Adopters - add a file adopters: organizations who use this project in production or test it https://clomonitor.io/docs/topics/checks/#adopters
• Code of Conduct - add a file code of conduct: https://clomonitor.io/docs/topics/checks/#code-of-conduct
• Contributing - add a file contributing: https://clomonitor.io/docs/topics/checks/#contributing
• Governance - add a file governance: https://clomonitor.io/docs/topics/checks/#governance
• Roadmap - add a file roadmap: https://clomonitor.io/docs/topics/checks/#roadmap
• Summary Table - add a summary table for NSM on CNCF landscape: https://github.com/cncf/landscape/blob/master/docs/item_summary.md

Best Practices

• Community meeting - add a link to community meetings in README.md: https://clomonitor.io/docs/topics/checks/#community-meeting

Security

• Security policy - add a file security: https://clomonitor.io/docs/topics/checks/#security-policy

Legal

• Trademark disclaimer - Website does not have the correct trademark disclaimer #277