Provide default configuration file

[io7m]

Maybe this:

<?xml version="1.0" encoding="UTF-8" ?>

<Configuration xmlns="urn:com.io7m.waxmill.config:1:0">
  <Paths>
    <Path type="ZFSExecutable"
          value="/sbin/zfs"/>
    <Path type="GRUBBhyveExecutable"
          value="/usr/local/sbin/grub-bhyve"/>
    <Path type="BhyveExecutable"
          value="/usr/sbin/bhyve"/>
    <Path type="CuExecutable"
          value="/usr/bin/cu"/>
    <Path type="VirtualMachineConfigurationDirectory"
          value="/etc/waxmill/vm"/>
    <Path type="VirtualMachineRuntimeDirectory"
          value="/storage/vm"/>
  </Paths>
</Configuration>

The problem is that we don't know which ZFS filesystem the user wants. Maybe a command-line option to specify this, and generate a config file?