Clarify MCP server toolset configuration (#58666)

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Anne-Marie <102995847+am-stead@users.noreply.github.com>

Author: 3 people

content/copilot/how-tos/use-copilot-agents/coding-agent/extend-coding-agent-with-mcp.md

@@ -310,14 +310,21 @@ If you want to allow {% data variables.product.prodname_copilot_short %} to acce
         "github-mcp-server": {
           "type": "http",
           // Remove "/readonly" to enable wider access to all tools.
-          // Then, use the "tools" key to specify the subset of tools you'd like to include.
+          // Then, use the "X-MCP-Toolsets" header to specify which toolsets you'd like to include.
+          // Use the "tools" field to select individual tools from the toolsets.
           "url": "https://api.githubcopilot.com/mcp/readonly",
-          "tools": ["*"]
+          "tools": ["*"],
+          "headers": {
+            "X-MCP-Toolsets": "repos,issues,users,pull_requests,code_security,secret_protection,actions,web_search"
+          }
         }
       }
     }
    ```
 
+
+For more information on toolsets, refer to the [README](https://github.com/github/github-mcp-server?tab=readme-ov-file#available-toolsets) in the {% data variables.product.github %} Remote MCP Server documentation.
+
 1. Click **Save**.
 {% data reusables.actions.sidebar-environment %}
 1. Click the `copilot` environment.