Update smsim-in-R.Rmd

First comments (before the "IPF in R")
I think the maximisation of entropy and maximum likelihood are similar, if not the same, concepts. Papers using the ML terminology include [this](http://linkinghub.elsevier.com/retrieve/pii/S019897150800080X) and [this](http://www.sciencedirect.com/science/article/pii/0167947393E00559). I've never fully understood maximum entropy either. Is it the values that maximise the number of ways that values can change a small amount while maintaining the same result? I don't think we need to go into too much detail on the theory. We should refer interested readers to more theoretical papers like this: http://www.sciencedirect.com/science/article/pii/0167947393E00559 and this: http://data.princeton.edu/wws509/notes/c5.pdf . I'm out of my depth here.