Link to serial port rules file for Linux users

[ctsexton]

Hi!
I was struggling to get the API working on Linux until I found this forum post and the accompanying serial port rules file: https://forum.sensel.com/t/morph-update-version-0-16-overlay-designer-beta-morph-settings-no-overlay-mpe-updates-xyz-midi-and-linux/315

Maybe it would be a good idea to include the rules file here somewhere, or at least a link to it in the README under the Linux heading?