Update broken link in README.md for keras VAE example code

[gaikwadrahul8]

I have updated broken link on this page for keras VAE example code under this paragraph "This example is a port of the code for a multilayer perceptron based variational autoencoder from this link https://github.com/keras-team/keras/blob/master/examples/variational_autoencoder.py See this tutorial for a description of how autoencoders work. " so please do the needful. Thank you!