Add nebulgym to the list, update nebullvm

[emilecourthoud]

Hi, I have added nebulgym to the list. It is a library that was released today!

It is a very user-friendly library that allows developers to speed up artificial intelligence training with only 2 lines of code. Nebulgym has some of the greatest optimization techniques running underneath it, which operate on the full training computing stack, from efficient data loading, to faster forward and backward passes, to earlier convergence.

Note that I've also updated nebullvm description. I'm a maintainer of both libraries, and now nebullvm will support many more optimization techniques than just deep learning compilers.

Cheers, Emile