Update docs/Learning-Environment-Design.md

Co-authored-by: Vincent-Pierre BERGES <vincentpierre@unity3d.com>

docs/Learning-Environment-Design.md

 Note, stepping manually is an advanced scenario and some care is required.
 If this is the case, be sure `Academy.Instance.EnvironmentStep()` is not called directly or indirectly by the agent's
 API e.g. from the `CollectObservations()`, `OnActionReceived`, and `Heuristic()` functions as this will
-cause an infinite loop that prevents the main Academy update function from being called.
+cause an infinite loop that prevents the main Unity `Update()` function from being called.
 
 ### Multiple Areas