How to Make a Calendar or Free/Busy Information Public in Google Calendar

"Never reveal a secret," Aristotle the great philosopher said to Alexander the Great, "to two.
If the information ever becomes public, you're in a bind: punish both and commit injury; or pardon both and forgive neither consciously."
Now, Bar Hebræus doesn't say so in his Laughable Stories, but it's clearly better to reveal the information to the public directly (if that's what you're after):
›› Want to share your team's schedule with the world or let everybody know when you're free? Here's how to publish a calendar's details or free/busy information publicly in Google Calendar.