Add gallery example demonstrating how to drop into HoloViews

## Request

Add Gallery example demonstrating the basics of dropping into HoloViews

## Motivation

A part of the elevator pitch of hvPlot is that you can easily drop into HoloViews and the rest of the ecosystem when needed.

But why this is useful and how to do this might not be very clear to new users that are not familiar with HoloViews.

I believe a gallery example would be very helpful.

A gallery example would also complement the elevator pitch if potential users tell me or other advocates to make the elevator pitch more concrete.