Adding tutorial on text mining surveys with r

Here's the result of my activities during the sprint, I look forward to review and feedback. 

Looking at the other PRs, I see this has a bit of overlap with the contribution from @emhart I didn't see that contribution listed amongst the projects on the [dc etherpad](https://etherpad.mozilla.org/sciencelab-2014summersprint-data-carpentry), we might have benefited from some coordination. Anyway, I think mine wins because it's free of wordclouds ;) Looks we're pitching at different levels of skill, I'm going for the novice and Ted is at the more experienced user, so perhaps coexistence is fine.