Add reference of univnet implementation

Author: Wonbin-Jung

Diff for: README.md

@@ -271,6 +271,7 @@ credit a few of the amazing folks in the community that have helped make this ha
 - [Ramesh et al](https://arxiv.org/pdf/2102.12092.pdf) who authored the DALLE paper, which is the inspiration behind Tortoise.
 - [Nichol and Dhariwal](https://arxiv.org/pdf/2102.09672.pdf) who authored the (revision of) the code that drives the diffusion model.
 - [Jang et al](https://arxiv.org/pdf/2106.07889.pdf) who developed and open-sourced univnet, the vocoder this repo uses.
+- [Kim and Jung](https://github.com/mindslab-ai/univnet) who implemented univnet pytorch model.
 - [lucidrains](https://github.com/lucidrains) who writes awesome open source pytorch models, many of which are used here.
 - [Patrick von Platen](https://huggingface.co/patrickvonplaten) whose guides on setting up wav2vec were invaluable to building my dataset.
 

Diff for: tortoise/models/vocoder.py

@@ -223,7 +223,11 @@ def remove_weight_norm(self):
 
 
 class UnivNetGenerator(nn.Module):
-    """UnivNet Generator"""
+    """
+    UnivNet Generator
+    
+    Originally from https://github.com/mindslab-ai/univnet/blob/master/model/generator.py.
+    """
 
     def __init__(self, noise_dim=64, channel_size=32, dilations=[1,3,9,27], strides=[8,8,4], lReLU_slope=.2, kpnet_conv_size=3,
                  # Below are MEL configurations options that this generator requires.