Explain how to change the scale for bivariate reference example

I would claim the scale of the example in the [`bivariate` reference example](https://hvplot.holoviz.org/reference/pandas/bivariate.html#pandas-gallery-bivariate) is not useful for "production".


By the way the scale is not explained. Me guess is that its some relative scale that sums to 1. But I am not sure as it is not explained.

If I was to hand this plot over to any one else I would have to explain the scale and probable change it to something easier to read for many people. Business managers would like something closer to small integers than tiny floats I would claim.

My request is to get the scale explained in the reference documentation and improve the example to make it useful by showing how to adjust the scale to something more readable.