Update README.md

Author: twishabansal

packages/toolbox-core/README.md

@@ -463,6 +463,9 @@ async with ToolboxClient("http://127.0.0.1:5000") as toolbox:
     print(result)
 ```
 
+> [!NOTE]
+> An auth token getter for a specific name (e.g., "GOOGLE_ID") will replace any client header with the same name followed by "_token" (e.g., "GOOGLE_ID_token").
+
 ## Binding Parameter Values
 
 The SDK allows you to pre-set, or "bind", values for specific tool parameters