Add doc links to Dangerbot to explain reviewer roulette in more detail

danger/roulette/Dangerfile

@@ -16,6 +16,10 @@ To spread load more evenly across eligible reviewers, Danger has randomly picked
 a candidate for each review slot. Feel free to override this selection if you
 think someone else would be better-suited, or the chosen person is unavailable.
 
+To read more on how to use the reviewer roulette, please take a look at the
+[Engineering workflow](https://about.gitlab.com/handbook/engineering/workflow/#basics)
+and [code review guidelines](https://docs.gitlab.com/ee/development/code_review.html).
+
 Once you've decided who will review this merge request, mention them as you
 normally would! Danger does not (yet?) automatically notify them for you.