Add github releases

[MorsMortium]

Hi! I am trying to package extensions I use, on the Arch User repository (AUR), for LibreWolf. This is so me and others can download and install the extension without the mozilla website. For this it is needed that the exact same file be available for download (Firefox does not run extensions that are not verified already). It would be enough if just the version number and the xpi file was made available, per release, no need for a description or change log.