update readme.md

readme.md

@@ -35,6 +35,13 @@ If this is your first time installing the Portal add-on, you will need to instal
 - Select `Connection Type` from the dropdown menu.
 - Click `Start Server` to start the server.
 
+### Custom Handlers
+You can create custom handlers to manipulate the data that is received. To do this, follow these steps:
+1. Copy and paste the [template code](/templates/custom_data_handler.py) into blender's text editor.
+2. Modify the `custom_data_handler` function with your custom logic.
+3. Run the script to register the custom handler.
+4. Locate the `Portal.custom` panel in the `3D View` sidebar.
+
 
 ## Documentation
 For more information, visit the [Portal](https://github.com/sean1832/portal).