Add to AUR (arch user repository)

[dz0ny]

Describe the solution you'd like
A way to install package via AUR.

Additional context
Requested in #36

[dz0ny]

pkgname=<pkgname>
pkgver=1.0.0
pkgrel=1
pkgdesc="Description of your app"
arch=('x86_64' 'aarch64')
url="https://github.com/<user>/<project>"
license=('MIT')
depends=('cairo' 'desktop-file-utils' 'gdk-pixbuf2' 'glib2' 'gtk3' 'hicolor-icon-theme' 'libsoup' 'pango' 'webkit2gtk-4.1')
options=('!strip' '!emptydirs')
install=${pkgname}.install
source_x86_64=("${url}/releases/download/v${pkgver}/appname_${pkgver}_amd64.deb")
source_aarch64=("${url}/releases/download/v${pkgver}/appname_"${pkgver}_arm64.deb")