Updated the release branch docs (#3621)

* Updated the release branch docs

* Edited the README

Author: vincentpierre

README.md

@@ -29,23 +29,23 @@ developer communities.
 * Unity environment control from Python
 * 15+ sample Unity environments
 * Two deep reinforcement learning algorithms,
-[Proximal Policy Optimization](https://github.com/Unity-Technologies/ml-agents/tree/latest_release/docs/Training-PPO.md)
- (PPO) and [Soft Actor-Critic](https://github.com/Unity-Technologies/ml-agents/tree/latest_release/docs/Training-SAC.md)
+[Proximal Policy Optimization](docs/Training-PPO.md)
+ (PPO) and [Soft Actor-Critic](docs/Training-SAC.md)
  (SAC)
 * Support for multiple environment configurations and training scenarios
 * Self-play mechanism for training agents in adversarial scenarios
 * Train memory-enhanced agents using deep reinforcement learning
 * Easily definable Curriculum Learning and Generalization scenarios
-* Built-in support for [Imitation Learning](https://github.com/Unity-Technologies/ml-agents/tree/latest_release/docs/Training-Imitation-Learning.md) through Behavioral Cloning or Generative Adversarial Imitation Learning
+* Built-in support for [Imitation Learning](docs/Training-Imitation-Learning.md) through Behavioral Cloning or Generative Adversarial Imitation Learning
 * Flexible agent control with On Demand Decision Making
 * Visualizing network outputs within the environment
 * Wrap learning environments as a gym
 * Utilizes the Unity Inference Engine
 * Train using concurrent Unity environment instances
 
 ## Releases & Documentation
-**Our latest, stable release is 0.14.1. Click
-[here](https://github.com/Unity-Technologies/ml-agents/tree/latest_release/docs/Readme.md) to
+**Our latest, stable release is 0.15.0. Click
+[here](docs/Readme.md) to
 get started with the latest release of ML-Agents.**
 
 The table below lists all our releases, including our `master` branch which is under active
@@ -61,8 +61,7 @@ details of the changes between versions.
 
 | **Version** | **Release Date** | **Source** | **Documentation** | **Download** |
 |:-------:|:------:|:-------------:|:-------:|:------------:|
-| **master** (unstable) | -- | [source](https://github.com/Unity-Technologies/ml-agents/tree/master) |  [docs](https://github.com/Unity-Technologies/ml-agents/tree/master/docs/Readme.md) | [download](https://github.com/Unity-Technologies/ml-agents/archive/master.zip) |
-| **0.14.1** (latest stable release) | February 26, 2020 | **[source](https://github.com/Unity-Technologies/ml-agents/tree/latest_release)** |  **[docs](https://github.com/Unity-Technologies/ml-agents/tree/latest_release/docs/Readme.md)** | **[download](https://github.com/Unity-Technologies/ml-agents/archive/latest_release.zip)** |
+| **0.14.1** | February 26, 2020 | [source](https://github.com/Unity-Technologies/ml-agents/tree/0.14.1) |  [docs](https://github.com/Unity-Technologies/ml-agents/tree/0.14.1/docs/Readme.md) | [download](https://github.com/Unity-Technologies/ml-agents/archive/0.14.1.zip) |
 | **0.14.0**  | February 13, 2020 | [source](https://github.com/Unity-Technologies/ml-agents/tree/0.14.0) |  [docs](https://github.com/Unity-Technologies/ml-agents/tree/0.14.0/docs/Readme.md) | [download](https://github.com/Unity-Technologies/ml-agents/archive/0.14.0.zip) |
 | **0.13.1**  | January 21, 2020 | [source](https://github.com/Unity-Technologies/ml-agents/tree/0.13.1) |  [docs](https://github.com/Unity-Technologies/ml-agents/tree/0.13.1/docs/Readme.md) | [download](https://github.com/Unity-Technologies/ml-agents/archive/0.13.1.zip) |
 | **0.13.0**  | January 8, 2020 | [source](https://github.com/Unity-Technologies/ml-agents/tree/0.13.0) |  [docs](https://github.com/Unity-Technologies/ml-agents/tree/0.13.0/docs/Readme.md) | [download](https://github.com/Unity-Technologies/ml-agents/archive/0.13.0.zip) |

com.unity.ml-agents/CHANGELOG.md

@@ -5,7 +5,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
 
-## [Unreleased]
+## [0.15.0-preview] - 2020-03-18
 ### Major Changes
  - `Agent.CollectObservations` now takes a VectorSensor argument. (#3352, #3389)
  - Added `Agent.CollectDiscreteActionMasks` virtual method with a `DiscreteActionMasker` argument to specify which discrete actions are unavailable to the Agent. (#3525)

docs/Migrating.md

@@ -7,7 +7,7 @@ The versions can be found in
 
 # Migrating
 
-## Migrating from 0.14 to latest
+## Migrating from 0.14 to 0.15
 
 ### Important changes
 * The `Agent.CollectObservations()` virtual method now takes as input a `VectorSensor` sensor as argument. The `Agent.AddVectorObs()` methods were removed.