2D demo of Prolific Dreamer

[yuanzhi-zhu]

Thank you so much for this great work.

I just made a 2D demo of Prolific Dreamer with VSD loss (SDS loss is also supported) here for those who are interested.

Given that this repo is *three*studio, I guess you have no intention of including a 2D playground in this repository? Then would it be possible to just add a link to the 2D demo in your readme.md :p