The `chatSkills` contribution point is missing in `contribution-points.md`

[tamuratak]

The chatSkills contribution point is missing in contribution-points.md. It is explained only in agent-skills.md.

• https://github.com/microsoft/vscode-docs/blob/main/api/references/contribution-points.md
• https://github.com/microsoft/vscode-docs/blob/main/docs/copilot/customization/agent-skills.md#register-the-skill-in-packagejson

[ritik4ever]

Hi, I'd like to work on this issue. Is it okay if I take this?