Some information in the GDScript documentation page was outdated (like
it still treats Zed if it was a macOS exclusive app) or some details
were missing.

- The `zed-gdscript` URL has been updated with the new owner.
- Pre-requisites added (with netcat included).
- Godot installation steps removed, it's now listed in the
pre-requisites.
- Setup steps simplified and reworded.

The note at the bottom was removed as I didn't see the issue in my end.

Release Notes:

- N/A