Transformation partner selection page

A draft of a page describing what a department might be looking for when selecting a technical transformation partner. It's not ready yet, but I wanted to make a start on the pull request so people can start looking at it. Still to do:
* Is this the right place for the page to live?
* I can't work out how to get the index page working.
* This page was originally written as a stand-alone document, so it duplicates content available elsewhere in the service manual.
* There's a lot of opportunity for linking to other sections of the service manual.
* Probably lots more.