Add link to curriculum docs in learning environment design (#4687)

docs/Learning-Environment-Design.md

 important to ensure that your environment parameters are updated at each step to
 the correct values. To enable this, we expose a `EnvironmentParameters` C# class
 that you can use to retrieve the values of the parameters defined in the
-training configurations for both of those features.
+training configurations for both of those features. Please see our
+[documentation](Training-ML-Agents.md#environment-parameters)
+for curriculum learning and environment parameter randomization for details.
 
 We recommend modifying the environment from the Agent's `OnEpisodeBegin()`
 function by leveraging `Academy.Instance.EnvironmentParameters`. See the