Added link to knitr intro

[sachsmc]

No description provided.

[seankross]

You're going to need to go into your git repository to execute the following commands:

git remote add --track master dss https://github.com/DataScienceSpecialization/DataScienceSpecialization.github.io.git
git fetch dss
git merge dss/master
git push

After that I should be able to merge this pull request.