Update README.md

Author: jeewenjie

README.md

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 Download trained weights here: https://www.dropbox.com/s/2ytshnr5iavax2q/728467-2001.data-00000-of-00001?dl=0
 
+Put downloaded weights into ./checkpoints.
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 # Improved Speech Enhancement with the Wave-U-Net
 
 The [Wave-U-Net applied to speech enhancement](http://arxiv.org/abs/1811.11307) [1], an adaptation of the [original implementation](https://github.com/f90/Wave-U-Net) for music source separation by [Stoller et al](https://arxiv.org/abs/1806.03185) [2].