Release video recorder (#1978)

* Add GetTotalStepCount to the Academy

This will allow the RecordVideos plugin to record based on the current academy step

* fixup! Add GetTotalStepCount to the Academy

* Add the video recorder to the documentation

docs/Readme.md

     [Learning](Learning-Environment-Design-Learning-Brains.md)
 * [Learning Environment Best Practices](Learning-Environment-Best-Practices.md)
 * [Using the Monitor](Feature-Monitor.md)
+* [Using the Video Recorder](https://github.com/Unity-Technologies/video-recorder)
 * [Using an Executable Environment](Learning-Environment-Executable.md)
 * [Creating Custom Protobuf Messages](Creating-Custom-Protobuf-Messages.md)