Instructions on setting an install's Appliance ID #486

[phillxnet]

Fixes #158 Fixes #486

This pull request's proposal

Provide an 'About Appliance ID' Guide to:

• Inform users of the Appliance ID's purpose.
• Empower self-configuration: for what-ever reason.

Specifically head-off pre-conceptions re code fingerprinting. We are a free software project and simply require a means to uniquely identify an install for non-nefarious open technical purposes.

Checklist

• [x] With the proposed changes no Sphinx errors or warnings are generated.
• [x] I have added my name to the AUTHORS file, if required (descending alphabetical order).

[phillxnet]

@FroggyFlox & @Hooverdan96 As this is a dependency of ongoing authoring re #496 I'l like to merge shortly. Unless of course there are any objections. No worries if no time is available. Just wanted to make you both aware of this long awaited doc addition.

Re our OEM relevant preparations, I wanted to have a canonical reference for exactly what our Appliance ID actually is.

[phillxnet]

@Hooverdan96 Thanks for all the suggestions. Much appreciated. I've popped them in, with commit message attribution. I'll merge and publish to remove the blocker on the linked OEM doc development.