Fixed text in GettingStarted page specifying the logdir for tensorboard. Before it was in a directory summaries which no longer existed. Results are now saved to the results dir. (#4085)

docs/Getting-Started.md

 ### Observing Training Progress
 
 Once you start training using `mlagents-learn` in the way described in the
-previous section, the `ml-agents` directory will contain a `summaries`
+previous section, the `ml-agents` directory will contain a `results`
-tensorboard --logdir=summaries
+tensorboard --logdir=results
 ```
 
 Then navigate to `localhost:6006` in your browser to view the TensorBoard