Add initial FreeBSD script & installation doc (#30981)

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

---------

Co-authored-by: Peter Tripp <peter@zed.dev>

docs/src/SUMMARY.md

@@ -147,6 +147,7 @@
   - [macOS](./development/macos.md)
   - [Linux](./development/linux.md)
   - [Windows](./development/windows.md)
+  - [FreeBSD}(./development/freebsd.md)]
   - [Local Collaboration](./development/local-collaboration.md)
   - [Using Debuggers](./development/debuggers.md)
 - [Release Process](./development/releases.md)