### Context
This PR adds documentation for setting up GitHub Copilot Enterprise as
an edit prediction provider in Zed.
There was previously no documentation for this feature, which was
implemented in [PR
#32296](https://github.com/zed-industries/zed/pull/32296).
This follows up on [my
comment](https://github.com/zed-industries/zed/issues/22901#issuecomment-3034817471)
and the response from the[ Zed
team](https://github.com/zed-industries/zed/issues/22901#issuecomment-3034837282),
which clarified the required settings.
### What’s included
- Documents the `enterprise_uri` setting for Copilot Enterprise in
`edit-prediction.md`.
- Explains how to configure the setting and what to expect from the
sign-in flow.
### Notes
- This is a documentation-only change.
- No code or tests are affected.
Release Notes:
- N/A
---------
Co-authored-by: Peter Tripp <peter@zed.dev>
