Someone pointed out that while documentation in general is great, it's
important to include a "last updated date" in it.
This is because documentation usually far outlasts the thing it
documents, and so when we read it several years after it was written, it
be incorrect compared with the current state.
Placing a last updated date into the file enables future readers to be
aware that the information may be out of date.
Anyway, something to keep in mind as we continue to make more good docs!