chore: add PKGBUILD for local pacman installation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

PKGBUILD

@@ -0,0 +1,16 @@
+pkgname='discordo-plus'
+pkgver='1.0.0'
+pkgrel=1
+pkgdesc='Discord TUI client (fork)'
+arch=('x86_64')
+depends=('mpv')
+optdepends=('xdotool: X11 geometry detection')
+
+build() {
+  cd "$startdir"
+  go build -o discordo-plus .
+}
+
+package() {
+  install -Dm755 "$startdir/discordo-plus" "$pkgdir/usr/local/bin/discordo-plus"
+}