README figure is low-res and transparent

[talonchandler]

The latest README figure is lower resolution than the previous one, so the smallest text is barely legible:

@ziw-liu also pointed out that the background is mostly transparent and inconsistent:

the equation in the figure is on a solid white background, while the rest of the figure is on a transparent background that may have contrast issues in a dark theme

@mattersoflight can you point me to the source file or fix these when you get a chance?

Note: this does not need to be fixed before the release, since I'm linking the github file directly (I learned through recOrder releases that linking the github file is a good strategy since distributing .pngs is suboptimal---no need to pip-install big pngs for everyone).

[mattersoflight]

Sorry for the delay @talonchandler- here the source PDF on our google drive. The folder Figure_Apr2022 has all the other figures too.

@ziw-liu pointed me to the trick to show different images when the github theme changes, which I think is the way to go for all READMEs.

[ziw-liu]

the trick to show different images when the github theme changes

Example in viscy: mehta-lab/VisCy#22 (comment)

Edit: for reference I generated those by applying Filters -> Color -> Invert -> Invert lightness in Inkscape.