London system trap

What is that trap in the London system by which one can capture the opponents' queen almost regardless of what the opponent plays?

In doc/OpeningsAndDefenses.md, find the paragraph

> Even if Black does not play d5 or Nf6, it is still possible for White to set up a neat trap in a which an early check leads to queen capture by causing the [FINISH WRITING]

and edit it to describe the trap. Chris showed it to me last week but I don't quite remember how it goes.

Pull request for this issue may have more than one commit, affecting only the aforementioned file and maybe adding one or two diagram files to the diagrams/openings folder.