Add this repo to the official Kicad plugins manager

[Alarm-Siren]

See here for instructions: https://dev-docs.kicad.org/en/addons/

This will necessarily break backwards compatibility due to the structural folder changes, so is being reserved for version 4.0.0.

It will also require a significant re-write of the readme file.

[Alarm-Siren]

Need to change the folder structure to match the following:

|- footprints
   |- first-library.pretty
      |- my-footprint.kicad_mod
      |- ...
|- symbols
      |- my-symbols.kicad_sym
      |- ...
|- resources
   |- icon.png
|- metadata.json```

[Alarm-Siren]

Will need to create a metadata.json file, and create an icon.png (64x64 pixels).

[Alarm-Siren]

footprint connection references in the symbols will need to be updated to match the new names, and instructions given in the README file will need to be updated (both for manual and Plugin Manager installation).

Note that the plugin manager does not automatically add the downloaded library to the Project Libraries; that still has to be done manually.

[Alarm-Siren]

Namespace to be com.github.alarm-siren.arduino-kicad-library