chore: fix presentation

presentation/presentation.md

@@ -134,11 +134,23 @@ end
 
 ## Safety
  - If a game state exists, then it was created by a user
- - The game state can not divert.
+ - The game state cannot divert.
 
 ## Liveness
  - Eventually all users will have the same game state
 
 --- 
 
+## Interface
+
+```elixir
+receive do
+  {:start_game, paticipants} -> {:new_game, game, game_state}
+  {:make_move, game, participant, move} -> {:update_game, game, game_state} or {:game_finished, game}
+  {:get_game_state, game} -> {:game_state, game, game_state}
+end
+```
+
+---
+
 #### Questions?