configs/releng: add and enable ModemManager

ModemManager's mmcli is the simplest way to connect with WWAN modems.

Mention mmcli in MOTD.

Implements #110.

configs/releng/airootfs/etc/motd

@@ -2,7 +2,8 @@ To install Arch Linux follow the installation guide:
 https://wiki.archlinux.org/index.php/Installation_guide
 
 For Wi-Fi, authenticate to the wireless network using the iwctl utility.
-Ethernet and Wi-Fi connections using DHCP should work automatically.
+For mobile broadband (WWAN) modems, connect with the mmcli utility.
+Ethernet, WLAN and WWAN interfaces using DHCP should work automatically.
 
 After connecting to the internet, the installation guide can be accessed
 via the convenience script Installation_guide.

configs/releng/airootfs/etc/systemd/system/dbus-org.freedesktop.ModemManager1.service

+/usr/lib/systemd/system/ModemManager.service
\ No newline at end of file

configs/releng/airootfs/etc/systemd/system/multi-user.target.wants/ModemManager.service

+/usr/lib/systemd/system/ModemManager.service
\ No newline at end of file

configs/releng/packages.x86_64

@@ -57,6 +57,7 @@ memtest86+
 mkinitcpio
 mkinitcpio-archiso
 mkinitcpio-nfs-utils
+modemmanager
 mtools
 nano
 nbd