Add use curiosity in Hallway example environment (#1952)

docs/Learning-Environment-Examples.md

     `VisualHallway` scene.
 * Reset Parameters: None.
 * Benchmark Mean Reward: 0.7
+  * To speed up training, you can enable curiosity by adding `use_curiosity: true` in `config/trainer_config.yaml`
 * Optional Imitation Learning scene: `HallwayIL`.
 
 ## [Bouncer](https://youtu.be/Tkv-c-b1b2I)