This PR removes the Repology badge from the README.

At time of writing, the majority of the packages listed here are
woefully out of date:

<img width="299" alt="Screenshot 2025-05-17 at 8 44 16 AM"
src="https://github.com/user-attachments/assets/c45afba3-72ac-488d-a067-1fb0e237c7c0"
/>

This isn't a good look for someone coming to the Zed repository for the
first time.

I've added a link to the Repology list in the "Linux" section of the
docs for people who are interested in checking the packaging status in
various repos.

Release Notes:

- N/A