Adding correct links for migration guide.

docs/Migrating.md

 * The training script `ppo.py` and `PPO.ipynb` Python notebook have been
   replaced with a single `learn.py` script as the launching point for training
   with ML-Agents. For more information on using `learn.py`, see
-  [here](Training-ML-Agents.md).
+  [here](Training-ML-Agents.md#training-with-mlagents-learn).
-  [here](Training-ML-Agents.md).
+  [here](Training-ML-Agents.md#training-config-file).
 
 ### Unity API