DOC: Point to step in stairs plot-type entry #27194

I think we could make stairs/step a bit easier to navigate by adding a drop of roadmapping by changing the intro sentence in the stairs plot type entry:

to something that sets expectations for stairs and points folks to steps when appropriate. Something like:

See `~matplotlib.axes.Axes.stairs` when plotting $y$ between $(x_i, x_{i+1})$ and ~`matplotlib.axes.Axes.step` when plotting $y$ at $x$.  

Kinda like how pcolormesh has a little descriptor https://matplotlib.org/devdocs/plot_types/arrays/pcolormesh.html#sphx-glr-plot-types-arrays-pcolormesh-py
Originally posted by @story645 in #26233 (review)