add coursera courses on statistical modelling

[nandaloo]

Here are three freely available courses on background and practive of statistical modelling and in particular sampling based inference methods. I believe this is very valuable as an introduction.

https://www.coursera.org/learn/bayesian-statistics

https://www.coursera.org/learn/mcmc-bayesian-statistics

https://www.coursera.org/learn/mixture-models

I suggest to add this the repository.