Link to prelude reference page at the end of tutorial

Author: hedyhli

content/learn.md

@@ -433,3 +433,5 @@ An advantage of `Begin` over traditional programming languages' break and return
 ## End
 
 Nope, there isn't an `End` function. This is just the end of the tutorial.
+
+Check out the [prelude](/reference/prelude/) to continue exploring.