Support ArchLinux level-2 enroll; Add intune-portal pkg; Add instructions & FAQ

This PR adds necessary package & instructions to support level-2 enrollment on ArchLinux. Manjaro Linux is still pending for testing.

intune-portal/PKGBUILD

@@ -24,6 +24,8 @@ package() {
   ar x source.deb
   tar xvzf data.tar.gz
   cp -r "$srcdir/usr" "$pkgdir/"
+
+  ln -s ../../opt/microsoft/intune/bin/intune-portal "$pkgdir/usr/bin/intune-portal"
 }