Migration doc fixes

docs/Migrating.md

 ## Migrating from ML-Agents toolkit v0.7 to v0.8
 
 ### Important Changes
-* We have split the Python packges into two seperate packages `ml-agents` and `ml-agents-envs`
+* We have split the Python packges into two seperate packages `ml-agents` and `ml-agents-envs`.
+* `--worker-id` option of `learn.py` has been removed, use `--base-port` instead if you'd like to run multiple instances of `learn.py`.
 
 #### Steps to Migrate
 * If you are installing via PyPI, there is no change.
 
 ### Important Changes
 
-* Brains are now Scriptable Objects instead of MonoBehaviors. 
+* Brains are now Scriptable Objects instead of MonoBehaviors.
-  __Note:__ You can pass the same Brain to multiple agents in a scene by 
+  __Note:__ You can pass the same Brain to multiple agents in a scene by
 leveraging Unity's prefab system or look for all the agents in a scene
 using the search bar of the `Hierarchy` window with the word `Agent`.
 
-* We removed the `Broadcast` checkbox of the Brain, to use the broadcast 
+* We removed the `Broadcast` checkbox of the Brain, to use the broadcast
-* When training multiple Brains at the same time, each model is now stored 
+* When training multiple Brains at the same time, each model is now stored
-  graph scopes. 
+  graph scopes.
 * The **Learning Brain** graph scope, placeholder names, output names and custom
   placeholders can no longer be modified.
 
   * Agents have a `Brain` field in the Inspector, you need to drag the
     appropriate Brain ScriptableObject in it.
   * The Academy has a `Broadcast Hub` field in the inspector, which is
-    list of brains used in the scene.  To train or control your Brain 
-    from the `mlagents-learn` Python script, you need to drag the relevant 
-    `LearningBrain` ScriptableObjects used in your scene into entries 
+    list of brains used in the scene.  To train or control your Brain
+    from the `mlagents-learn` Python script, you need to drag the relevant
+    `LearningBrain` ScriptableObjects used in your scene into entries
     into this list.
 
 ## Migrating from ML-Agents toolkit v0.4 to v0.5

gym-unity/setup.py

       author_email='ML-Agents@unity3d.com',
       url='https://github.com/Unity-Technologies/ml-agents',
       packages=find_packages(),
-      install_requires=['gym', 'mlagents_envs']
+      install_requires=['gym', 'mlagents_envs==0.8.0']
       )