Add some basic user documentation for the import/export tool

This document probably (nay, certainly) needs some review from the
docs team.  Additionally, this document is currently not linked
to from any of the other content.  It should probably be linked
from the upgrade.markdown, and perhaps from the FAQ as well?
Add `sudo` to example sbin commands
Add links to `migrate` docs from other relevant places
Add command-prompt `$ ` prefix to example commands
Merge pull request #460 from cprice-puppet/feature/master/import-export-user-docs

Add some basic user documentation for the import/export tool