[docs] Update 'Record Demonstrations' documentation (#4432)

* [docs] Update 'Record Demonstrations' documentation

Updates a screenshot and documentation to include the newer `Num Steps To Record` field.

docs/Learning-Environment-Design-Agents.md

 <p align="center">
   <img src="images/demo_component.png"
        alt="Demonstration Recorder"
-       width="450" border="10" />
+       width="650" border="10" />
-for imitation learning. When you have recorded enough data, end the Editor play
-session. A `.demo` file will be created in the `Assets/Demonstrations` folder
-(by default). This file contains the demonstrations. Clicking on the file will
+for imitation learning. To specify an exact number of steps you want to record
+use the `Num Steps To Record` field and the editor will end your play session
+automatically once that many steps are recorded. If you set `Num Steps To Record`
+to `0` then recording will continue until you manually end the play session. Once
+the play session ends a `.demo` file will be created in the `Assets/Demonstrations`
+folder (by default). This file contains the demonstrations. Clicking on the file will
 provide metadata about the demonstration in the inspector.
 
 <p align="center">
 </p>
 
-You can then specify the path to this file in your training configurations.
+You can then specify the path to this file in your
+[training configurations](Training-Configuration-File.md#behavioral-cloning).