Add more links to useful resources
Add a link describing the `boot.cmd` format.
Install kernel modules

Without this step — with the .config provided by xen-arm-builder — the
bridge interface would not start because the `bridge` module would not
be present.
Merge pull request #215 from Chris00/modules

Install kernel modules
Merge pull request #214 from Chris00/more_links

Add more links to useful resources
Be more system agnostic w.r.t. cross compilation