Add license

[xandergos]

Please consider adding an open-source license (e.g MIT) so this code can be used in open source projects. Great work!

[nick-bvc]

The license situation is complicated. The code is built on the official StyleGAN3 release which has a nasty nvidia license that disallows relicensing to MIT

[hjk92g]

I am using your repo and planning to release the modified repo later.
Files in the R3GAN folder (e.g. R3GAN/Trainer.py) are rebranded and seem original from the authors (not from NVIDIA). Could the authors give a license for these? (I am a novice in licensing, but at least ChatGPT says it is okay to give different licenses for your original files)