Update r-resources.md

I learned R by following Hadley Wickham's and his fellow academicians' digital trail around the internet. Is it appropriate to add blogs to this list of resources? If so, would it be under a new category? 

packages:
btw, R refers to libraries as packages
adding R packages plr, and ggplot2. basically equivalent to python's pandas. 

books:
Data Analysis and Graphics Using R: An Example-Based Approach --- great, example based classic

talks: 
Eng data analysis with R -- hour long, excellent intro to practical analysis