heat series documentation improvement for format.

**My Improvement**

the add_heat_series documentation is not very thorough. I wanted to make a heat-series plot _without_ the text, but I couldn't find an option to do that. I started looking through other sections of the documentation to try and adjust fonts and such, but to no avail. I now realize there was a format option in the function, but that option was not explained in any detail. If there had been some text explaining that format controlled the text displayed on the heat-series, I could have saved an hour of time.

I want to add that I have really been enjoying this package! I just wish the documentation was more clear.
**Necessary Assets**
My heat series before changing format. It's view was disrupted by the display of numbers at the center of each cell/pixel.

View after adjusting format. I thought I had to adjust a font or change a series to make this improvement. If the documentation had been more clear, I would be much happier.

For information, I was looking at documentation through this link: https://dearpygui.readthedocs.io/en/latest/reference/dearpygui.html