Add flax logo in SVG format

[Ritobrata Ghosh]

Hi,

It would be really helpful if you add a logo for the Flax library.

A similar request was made for JAX here on Issue#4389 and was granted in this commit.

It would be really helpful to have an official Flax logo.

[Andreas Steiner]

@8bitmp3 who was working on the SVG logo recently IIRC

[Marc van Zee]

@8bitmp3 @avital Do you perhaps have the logo in SVG format?

[8bitmp3]

Nice @levskaya 👍