Add a snippet for my ad-hoc time-tracking system

because I'm finally using it again after a year or so, and thought
"Typing these out manually is stupid", and "I never have learned how to
write my own snippets."

Quite a bit later than I expected, I got it working.

...why yasnippet's "new snippet" feature defaults to type: command is
beyond me, and it caused me quite a bit of grief. Looks like that's not
true in current trunk, though. Guess I should try upgrading.