Readme Update for #874 (#911)

Updates readme to improve YouTube.on_progress() and Stream.download() documentation

README.md

@@ -228,12 +228,19 @@ If your application requires post-processing logic, pytube allows you to specify
 Similarly, if your application requires on-download progress logic, pytube exposes a callback for this as well:
 
 ```python
- >>> def show_progress_bar(stream, chunk, file_handle, bytes_remaining):
+ >>> def show_progress_bar(stream, chunk, bytes_remaining):
          return  # do work
 
  >>> yt.register_on_progress_callback(show_progress_bar)
 ```
 
+Download video(s) to specific directory with specific name
+
+```python
+>>> yt = YouTube('https://youtube.com/watch?v=2lAe1cqCOXo')
+>>> yt.streams.first().download(output_path="/tmp" ,filename='output')
+```
+
 ## Command-line interface
 
 pytube also ships with a tiny cli interface for downloading and probing videos.