Merge pull request #355 from RasaHQ/small-docs-fix

Small docs fix.

docs/docs/sdk-actions.mdx

@@ -85,6 +85,7 @@ your bot could execute the action `ActionCheckRestaurants`,
 which might look like this:
 
 ```python
+from typing import Text, Dict, Any, List
 from rasa_sdk import Action
 from rasa_sdk.events import SlotSet