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/x.install

+post_upgrade() {
+    # Restart polkit to get any new authorization actions we put down
+    systemctl restart polkit.service 2>/dev/null
+}
+
+post_install() {
+    if [ -d /run/systemd/system ] ; then
+        systemd-tmpfiles --create intune.conf
+    fi
+
+    systemctl --system daemon-reload
+    systemctl enable intune-daemon.socket --now
+
+    post_upgrade
+
+    echo "Please run: systemctl enable --now --user intune-agent.timer" 1>&2
+}
+
+pre_remove()
+{
+    systemctl disable intune-daemon.socket --now
+}
+
+pre_upgrade() {
+    pre_remove
+}
+
+post_remove() {
+    systemctl --system daemon-reload
+}
+