Add the advanced contrast limits widget to the Image layer tutorial

[psobolewskiPhD]

🧰 Task

This section is dedicated to adjusting contrast limits, but doesn't mention the advanced contrast limits widget that is available when right-clicking on the contrast limits slider in the layer controls.
https://napari.org/stable/howtos/layers/image.html#adjusting-contrast-limits

As far as I can tell the widget is just mentioned that you can access it here:
https://napari.org/stable/howtos/layers/image.html#controls