'Hello world' documentation

[joonas-fi]

Users could benefit from easy getting started docs

Like:

• Run $ sudo bluetoothctl
  • Type scan on
  • Find device with name beginning with PT-P... (the name is the Brother printer model name)
  • Type pair <bluetooth address> (where the address is something like EC:79:49:...)
• Then $ sudo rfcomm bind 0 <bluetooth address>
  • This should make /dev/rfcomm0 appear
• You need to have 128px high png (with alpha channel, i.e. transparency), you can use for testing: https://upload.wikimedia.org/wikipedia/commons/thumb/8/8a/Flatpak_Logo.svg/128px-Flatpak_Logo.svg.png