Add "Tidy Text Mining with R" (#2165)

CC BY-NC-SA

free-programming-books.md

@@ -1907,6 +1907,7 @@ For resources on Angular, Backbone, D3, Dojo, Ember, Express, jQuery, Knockout,
 * [The R Inferno](http://www.burns-stat.com/pages/Tutor/R_inferno.pdf) - Patrick Burns (PDF)
 * [The R Language](http://stat.ethz.ch/R-manual/R-patched/doc/html)
 * [The R Manuals](http://cran.r-project.org/manuals.html)
+* [Tidy Text Mining with R](http://tidytextmining.com/) - Julia Silge and David Robinson
 
 
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