doc: make it explicit that automake is needed to build LXD
doc: make it explicit that automake is needed to build LXD

This is useful mainly for those using apt's `--no-install-recommends`.

Signed-off-by: Simon Deziel <eca3f1a14b730e70ce4898287e4fc2f9966fa3a6@canonical.com>

lxc/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,lxc/lxd,hallyn/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,stgraber/lxd,stgraber/lxd,hallyn/lxd,lxc/lxd,lxc/lxd,lxc/lxd,stgraber/lxd,hallyn/lxd,hallyn/lxd,hallyn/lxd,hallyn/lxd