Add proper support for speaker notes

[jaspervdj]

You can configure patat to write the speaker notes for the current slide to a file whenever the slide changes:

patat:
  speakerNotes:
    file: /tmp/notes.txt

Then, you can display these in a second terminal (presumably on a second monitor) by just displaying this file whenever it changes. entr is one way to do that:

echo /tmp/notes.txt | entr -s 'clear; cat /tmp/notes.txt'

Alternatively, just use a second patat instance with --watch enabled:

patat -w /tmp/notes.txt