Tracking changes between specification releases

[joshuagl]

Clients should declare which version of the specification they implement and keep up-to-date with specification changes (see theupdateframework/python-tuf#1598), but we as the specification do not make it easy to understand what has changed between specification versions.

We might solve this a number of ways:

• link to the diff between current (n) and previous (n-1) release
• manually curate a change list
• ???

[mnm678]

A changelog has worked well for the Uptane Standard. It could be partially automated by using pr or commit names as a starting point.