document install-qibuild.sh usage on Arch
document install-qibuild.sh usage on Arch

Change-Id: Ib7c46cf49019eeb358d9b57ed0dc72bb3c131131

aldebaran/qibuild,dmerejkowsky/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild,dmerejkowsky/qibuild,dmerejkowsky/qibuild,dmerejkowsky/qibuild,aldebaran/qibuild,aldebaran/qibuild