Update documentation about disabling threading

docs/Training-PPO.md

 
 ### (Optional) Advanced: Disable Threading
 
-By default, PPO model updates can happen while the environment is being stepped. To disable this
-behavior, for instance to maintain strict
+By default, PPO model updates can happen while the environment is being stepped. This violates the
-experience-gathering, set `threaded` to `false`. Expect a slowdown of approximately 10-20% in
-training time if `threaded` is disabled.
+assumption of PPO slightly in exchange for a 10-20% training speedup. To maintain the
+strict on-policyness of PPO, you can disable parallel updates by setting `threaded` to `false`.
 
 Default Value: `true`