docs: Document setting up Claude in the Assistant (#13765)

Release Notes:
- Added documentation on how to set up Claude as the assistant.

---------

Co-authored-by: Peter Tripp <petertripp@gmail.com>
Co-authored-by: Gilles Peiffer <gilles.peiffer.yt@gmail.com>
Co-authored-by: Peter Tripp <peter@zed.dev>

docs/src/assistant-panel.md

@@ -134,6 +134,25 @@ You can use Ollama with the Zed assistant by making Ollama appear as an OpenAPI
   ```
 5. Restart Zed
 
+## Using Claude 3.5 Sonnet
+
+You can use Claude with the Zed assistant by adding the following settings:
+
+```json
+"assistant": {
+  "version": "1",
+  "provider": {
+    "default_model": "claude-3-5-sonnet",
+    "name": "anthropic"
+  }
+},
+```
+
+When you save the settings, the assistant panel will open and ask you to add your Anthropic API key.
+You need can obtain this key [here](https://console.anthropic.com/settings/keys).
+
+Even if you pay for Claude Pro, you will still have to [pay for additional credits](https://console.anthropic.com/settings/plans) to use it via the API.
+
 ## Prompt Library
 
 **Warning: This feature is experimental and the format of prompts is _highly_ likely to change. Use at your own risk!**