Release tf#android fix (#1180)

* The Android fix

* additional documentation

* added #

UnitySDK/Assets/ML-Agents/Scripts/CoreBrainInternal.cs

         public void InitializeCoreBrain(MLAgents.Batcher brainBatcher)
         {
 #if ENABLE_TENSORFLOW
-#if UNITY_ANDROID
+#if UNITY_ANDROID && !UNITY_EDITOR
 // This needs to ba called only once and will raise an exception if 
 // there are multiple internal brains
         try{

docs/Using-TensorFlow-Sharp-in-Unity.md

 
 ## iOS additional instructions for building
 
+* Before build your game against iOS platform, make sure you've set the
+  flag `ENABLE_TENSORFLOW` for it. 
 * Once you build the project for iOS in the editor, open the .xcodeproj file
   within the project folder using Xcode.
 * Set up your ios account following the
 TensorFlow's `freeze_graph.py`. The process to create such graph is explained in
 the [Using your own trained graphs](#using-your-own-trained-graphs) section.
 
-## Inside of Unity
+### Inside of Unity
 
 To load and use a TensorFlow data graph in Unity:
 
    your code :
 
    ```csharp
-   #if UNITY_ANDROID
+   #if UNITY_ANDROID && !UNITY_EDITOR
    TensorFlowSharp.Android.NativeBinding.Init();
    #endif
    ```