I would like to draw this diagram in tikz-cd. Specifically I would like the arrow to start 'from the top' of B here. I have looked at the example in the manual for tikz-cd, drawing the Snake Lemma, but it doesn't exactly explain anything well, and I have no idea what I'm doing regarding tikz in general. Is this easy at all to do?
To anyone asking why I would want to draw this diagram: I don't. I want to draw a diagram using similar arrows