To use this you need to create a .env file.
Example:

STREAM_KEY=Your Twitch stream key (example: aqwx-sl6k-0qq5-n65d-26s1)
VIDEO_SIZE=The size of the streamed video (example: 1920x1080)
BITRATE=The video bitrate (example: 5000)

This can be easily used to stream on YouTube too, just change the ingest variable to YouTube's stream URL and it should work just fine.