docs: Update git_hosting_providers setting documentation (#42129)

## Summary

Adds documentation for the `git_hosting_providers` setting that allows
users to configure custom self-hosted Git instances for clickable links.

## Description

This PR documents the previously undocumented `git_hosting_providers`
setting in the Git integration documentation. The setting allows users
to configure Zed to recognize and create clickable links to issues, pull
requests, and commits on self-hosted Git instances (like company GitLab
or GitHub Enterprise servers).

## Fixes

Closes #38433

## Test Plan

- Documentation follows the existing style and tone of `docs/src/git.md`
- Placement in the "Git Integrations" section makes logical sense
- Code example matches the format confirmed working by maintainers in
the issue

Release Notes:

- Improved: Documented the `git_hosting_providers` setting for
configuring custom self-hosted Git instances

---------

Co-authored-by: MrSubidubi <finn@zed.dev>

docs/src/git.md

@@ -249,7 +249,9 @@ Zed currently supports links to the hosted versions of
 
 ### Self-Hosted Instances
 
-For self-hosted GitHub, GitLab, or Bitbucket instances, add them to the `git_hosting_providers` setting so commit hashes and permalinks resolve to your domain:
+Zed automatically identifies Git hosting providers by checking for keywords in your Git remote URL. For example, if your self-hosted URL contains `gitlab`, `gitea`, or other recognized provider names, Zed will automatically register that hosting provider without any configuration needed.
+
+However, if your self-hosted Git instance URL doesn't contain identifying keywords, you can manually configure Zed to create clickable links to your instance by adding a `git_hosting_providers` setting so commit hashes and permalinks resolve to your domain:
 
 ```json [settings]
 {
@@ -263,7 +265,9 @@ For self-hosted GitHub, GitLab, or Bitbucket instances, add them to the `git_hos
 }
 ```
 
-Supported `provider` values are `github`, `gitlab`, `bitbucket`, `gitea`, `forgejo`, and `sourcehut`. The `name` field is optional and used for display purposes.
+The `provider` field specifies which type of hosting service you're using. Supported `provider` values are `github`, `gitlab`, `bitbucket`, `gitea`, `forgejo`, and `sourcehut`. The `name` is optional and used as a display name for your instance, and `base_url` is the root URL of your self-hosted server.
+
+You can configure multiple custom providers if you work with several self-hosted instances.
 
 ### Permalinks