Update README.md

Add download counter badge

Author: dshkol

README.md

@@ -2,6 +2,7 @@
 
 [![Build Status](https://travis-ci.org/mountainMath/cansim.svg?branch=master)](https://travis-ci.org/mountainMath/cansim)
 [![CRAN_Status_Badge](http://www.r-pkg.org/badges/version/cansim)](https://cran.r-project.org/package=cansim)
+[![CRAN_Downloads_Badge](https://cranlogs.r-pkg.org/badges/cansim)](https://cranlogs.r-pkg.org/badges/cansim)
 
 <a href="https://mountainmath.github.io/cansim/index.html"><img src="https://raw.githubusercontent.com/mountainMath/cansim/master/images/cansim-sticker.png" alt="cansim logo" align="right" width = "25%" height = "25%"/></a>