Document Windows-native command guidance

[caomengxuan666]

Summary

• add short notes for Windows-native command scope and option support
• link the notes from CONTRIBUTING.md without changing README
• document guidance from recent issue discussions so contributors have a clearer starting point when adding native commands

[crutkas]

@caomengxuan666 can you explain a bit more why this is needed? this feels very AI driven from a wording stance and want to deeper understand the needs for this.

[caomengxuan666]

I opened this because recent native-command PRs/issues like ps, kill, which, lsof, chown/chgrp all seem to run into the same discussion: should this command exist here, and what option scope is acceptable on Windows?

So I thought maybe it would be useful to leave a small contributor note saying: please discuss the scope first before opening a native-command PR.

But yeah, the current wording is probably too generic. Maybe I overdid it. I can trim it down a lot, or close this for now.