added R commands for poxplots in Q8c) in chapter 2

[rafaelschlatter]

Hi guys,

I added R code producing boxplots in question 8c) part iii) and iv) in chapter 2. The questions from the current version of the book ask for boxplots, but the present code produces scatterplots. Its four lines of code only, but I appreciate your feedback since I am new to GitHub (its my first pull request).

Regards, Rafael