update README

Author: jm12138

README.md

@@ -1,7 +1,7 @@
 # Paddle-MSSSIM
 
 ## Introduction
-* Fast and differentiable MS-SSIM and SSIM for Paddle.
+* Fast and differentiable MS-SSIM and SSIM for Paddle (This repo is based on [Pytorch MS-SSIM](https://github.com/VainF/pytorch-msssim) developed by @VainF).
 
     <img src="./images/lcs.png" width="25%">