Update the curiosity mention in Hallway (#3386)

docs/Learning-Environment-Examples.md

      training parameters.__
 * Float Properties: None
 * Benchmark Mean Reward: 0.7
-  * To speed up training, you can enable curiosity by adding `use_curiosity: true` in `config/trainer_config.yaml`
+  * To speed up training, you can enable curiosity by adding the `curiosity` reward signal in `config/trainer_config.yaml`
 
 ## [Bouncer](https://youtu.be/Tkv-c-b1b2I)