Written after each html build (conf.py build-finished hook) from
_templates/random_tip.html with the current list of tips; ?tip=<name> shows
a given one. Meant for e.g.
google-chrome --app=http://<host>:8095/did_you_know/random.html --window-size=560,460
Also shorten the picker tip's code lines to fit such a window.
