Update automations.rst (#1992)

Co-authored-by: Jesse Hills <3060199+jesserockz@users.noreply.github.com>

guides/automations.rst

@@ -270,6 +270,11 @@ global variables can be used to store the state of a garage door.
         type: int
         restore_value: no
         initial_value: '0'
+      # Example for global string variable
+      - id: my_global_string
+        type: std::string
+        restore_value: no  # Strings cannot be saved/restored
+        initial_value: '"hello world"'
 
    # In an automation
    on_press: