Adding a new article on R

[Notinm]

NOTE:

• Please fill out the template below

Did you read the instructions in the README?

Y

Have you read the instructions in CONTRIBUTING?

Y

Have you written this article by yourself? Have you taken inspiration from anywhere and then written it in your words?

Yes, I wrote it by myself. I had to review some articles online, but it's mostly what I know about R from what I saw in university :) I saw that there still wasn't an article on R on the Guides folder and I believe it's a useful complement.