Hey, I was wondering the same thing and went to ducment the solution in my cheatsheet. Thought i should share it here

x__min := -10: x__max := 20: y__min := -40: y__max := 40:
graph := plot(f(x), x = x__min .. x__max, y = y__min .. x__max):
arrow__1 := plots:-arrow([0, y__max], [0, 0.01], shape = arrow, head_width = 25/y__max, head_length = 20/x__max):
arrow__2 := plots:-arrow([x__max, 0], [0.01, 0], shape = arrow, head_width = 25/x__max, head_length = 20/y__max):
plots:-display(graph, arrow__1, arrow__2)

You can find an explanation and more info here: https://github.com/logicguy1/Maple-Cheatsheet#plots