Update README.md - photos, better sourcing info

[cunninghamsandwich]

Filing this to assign to myself:

Planning to update README.md with a more representative photo of the Authbox, more context around the design decisions, links to related projects like FATT, and optional part numbers for ordering complete kits from a manufacturer.

[thatch]

@brianredbeard and I have also discussed the need for "how to deploy" -- right now it's not on pypi, but could be if that makes things easier. I was originally aiming for a git-based deployment, something like

this repo ->
  some space's "blessed" upstream ->
    private repo with individual tools as branches with config checked in ->
      basically just copy to a raspi and enable at-boot

due to the distributed maintenance burden makerspaces typically see and the need for knowing what version should be reinstalled if an SD card goes bad. Open to other ideas.