This PR adds initial FreeBSD support for building Zed:
* Adds `script/freebsd` to install required dependencies on FreeBSD
* Adds `docs/freebsd.md` with build instructions and notes
* ⚠️ Mentions that `webrtc` is still **work-in-progress** on FreeBSD.
Related to : #15309
I’m currently working at discussions :
[Discussions](https://github.com/zed-industries/zed/discussions/29550)
Release Notes:
- N/A
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Co-authored-by: Peter Tripp <peter@zed.dev>
