Merge pull request #491 from Unity-Technologies/docs/broken-links

Fixed lingering broken links

CONTRIBUTING.md

 
 ### Communication
 
-First, please read through our [code of conduct](../CODE_OF_CONDUCT.md), 
+First, please read through our [code of conduct](CODE_OF_CONDUCT.md), 
 as we expect all our contributors to follow it.
 
 Second, before starting on a project that you intend to contribute

docs/Training-PPO.md

 
 If you are using curriculum training to pace the difficulty of the learning task presented to an agent, see [Training with Curriculum Learning](Training-Curriculum-Learning.md).
 
-For information about imitation learning, which uses a different training algorithm, see [Training with Imitation Learning](Training-Imitation-Learning).
+For information about imitation learning, which uses a different training algorithm, see [Training with Imitation Learning](Training-Imitation-Learning.md).
 
 ## Best Practices when training with PPO
 

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

 
 ![Internal Brain Inspector](images/internal_brain.png)
 
-See [Internal Brain](Learning-Environments-Design-External-Internal-Brains.md#internal-brain) for more information about using Internal Brains.
+See [Internal Brain](Learning-Environment-Design-External-Internal-Brains.md#internal-brain) for more information about using Internal Brains.
 
 If you followed these instructions well, the agents in your environment that use this brain will use your fully trained network to make decisions.