Include a file with requirements to speed up initial install

[nk9]

The script requires pyserial to be in the user's installed Python modules, but it doesn't explicitly discuss that in the README or provide a package manager file. I, for one, tried running it, then tried installing serial, and only then discovered that I needed to use pyserial.

It would be ideal to have a requirements.txt file so that those using a venv would get the requirement easily.