Add a Last Edited Date to Posts

With frequently changing information it can be useful to record both when a post was created and when it was last updated - showing that it’s been reviewed recently. We do this on this site by showing the created date and showing the last modified date if it’s different from the created date (see above the title). There’s two ways of doing this in Hugo: recording when you last changed it using the last changed date in Git (if you use it) (or a blend of the two)