Updating the master documentation with 0.15.1 release (#3708)

README.md

 * Train using concurrent Unity environment instances
 
 ## Releases & Documentation
-**Our latest, stable release is 0.15.0. Click
+**Our latest, stable release is 0.15.1. Click
 [here](https://github.com/Unity-Technologies/ml-agents/tree/latest_release/docs/Readme.md) to
 get started with the latest release of ML-Agents.**
 
 | **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) |
+| **0.15.1** | **March 30, 2020** | **[source](https://github.com/Unity-Technologies/ml-agents/tree/0.15.1)** | **[docs](https://github.com/Unity-Technologies/ml-agents/tree/0.15.1/docs/Readme.md)** | **[download](https://github.com/Unity-Technologies/ml-agents/archive/0.15.1.zip)** |
 | **0.15.0** | **March 18, 2020** | **[source](https://github.com/Unity-Technologies/ml-agents/tree/0.15.0)** | **[docs](https://github.com/Unity-Technologies/ml-agents/tree/0.15.0/docs/Readme.md)** | **[download](https://github.com/Unity-Technologies/ml-agents/archive/0.15.0.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) |

com.unity.ml-agents/CHANGELOG.md

 
 ### Minor Changes
  - Format of console output has changed slightly and now matches the name of the model/summary directory. (#3630, #3616)
- - Raise the wall in CrawlerStatic scene to prevent Agent from falling off. (#3650)
- - Fixed an issue where specifying `vis_encode_type` was required only for SAC. (#3677)
+ - Fixed an issue where exceptions from environments provided a returncode of 0. (#3680)
+ - Running `mlagents-learn` with the same `--run-id` twice will no longer overwrite the existing files. (#3705)
+
+## [0.15.1-preview] - 2020-03-30
+### Bug Fixes
+ - Raise the wall in CrawlerStatic scene to prevent Agent from falling off. (#3650)
+ - Fixed an issue where specifying `vis_encode_type` was required only for SAC. (#3677)
- - Fixed an issue where exceptions from environments provided a returncode of 0. (#3680)
- - Running `mlagents-learn` with the same `--run-id` twice will no longer overwrite the existing files. (#3705)
- - Fixed an issue where logging output was not visible; logging levels are now set consistently (#3703).
+ - Fixed an issue where logging output was not visible; logging levels are now set consistently. (#3703)
+
 
 ## [0.15.0-preview] - 2020-03-18
 ### Major Changes