Fix Readme example code for use with Gymnasium

README.md

@@ -59,6 +59,9 @@ For simplicity for installing ale-py with Gymnasium, `pip install "gymnasium[ata
 
 ```py
 import gymnasium as gym
+import ale_py
+
+gym.register_envs(ale_py)  # unnecessary but helpful for IDEs
 
 env = gym.make('ALE/Breakout-v5', render_mode="human")  # remove render_mode in training
 obs, info = env.reset()