Add subdomain specification documentation for AI agent

ai/agent.mdx

@@ -18,10 +18,20 @@
 
 To get started, add the agent to your Slack workspace and mention it with `@mintlify` in a channel.
 
+## Specify a subdomain
+
+If you have multiple documentation sites (such as public docs and customer docs), you can specify which subdomain the agent should work with by including the `subdomain` parameter in your message:
+
+- `@mintlify subdomain=public-docs` - Work with your public documentation
+- `@mintlify subdomain=customer-docs` - Work with your customer documentation  
+- `@mintlify subdomain=mintlify` - Work with a specific custom subdomain
+
+This ensures the agent makes changes to the correct documentation site when you have multiple subdomains configured.
+
 ## Add the agent to your Slack workspace
 
 <Note>
   If your Slack Workspace Owner requires admin approval to install apps, ask them to approve the Mintlify app before you connect it.
 </Note>
 
 1. Navigate to the [agent](https://dashboard.mintlify.com/products/agent) page of your dashboard.