Readme logo invisible in dark theme

[hathach]

Yeah, I use dark theme as well and have no idea how or which format to make it appeared nicely on both light and dark theme.

[dhalbert]

Here is a quick substitute image. The background of the original png is transparent. I made it white and added 10 pixels all around, because it was cropped very tightly.

@dhalbert, looks good. Make a PR

[hathach]

thanks @dhalbert , I have update readme with link to your image 👍 👍