Update Example section of Readme.md

[pronojitsaha]

@rhiever Readme.md has the tpot_mnist_pipeline.py (in the Example section) which is of a very early version. We have updated the tpot_mnist_pipeline.py in the tutorials section..but not done so in the Example of Readme.md. So I have updated the same including changing StratifiedShuffleSplit to train_test_split as discussed in #114

[coveralls]

Coverage remained the same at 28.741% when pulling d4a9dcc on pronojitsaha:master into 6860b92 on rhiever:master.

[rhiever]

I think all the extra models makes the example code look too complex. How about we just have the example code be a generated Random Forest call with 100+ estimators? That's usually what comes out of TPOT for the MNIST data set now anyway.

[pronojitsaha]

Yes, I was also thinking about the complexity to understand this for a first time user. I will look into it.

[coveralls]

Coverage remained the same at 28.741% when pulling d47e96b on pronojitsaha:master into 6860b92 on rhiever:master.

[rhiever]

Good to go! Cheers.