Update Preview release installation instructions (#11263)

Klaus Hipp created 

This PR updates the Homebrew installation instructions for the Preview
release, which has been migrated to ```homebrew/cask``` as
```zed@preview``` (see
[Commit](https://github.com/Homebrew/homebrew-cask/commit/bad25d79e13ca41b492c976ef70b72117c402d20)).

Release Notes:

- N/A

Change summary

README.md | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

Detailed changes

README.md 🔗 

@@ -23,8 +23,7 @@ brew install --cask zed
 Alternatively, to install the Preview release:
 
 ```sh
-brew tap homebrew/cask-versions

-brew install zed-preview

+brew install --cask zed@preview

 ```
 
 ## Developing Zed