improve wording of the bonus part

Co-authored-by: Colin Caine <[email protected]>

Author: golanor

exercises/practice/protein-translation/.docs/instructions.append.md

@@ -1,13 +1,19 @@
 # Instructions append
 
-This is a good exercise to experiment with non-standard string literals.
+## Bonus
 
-A short introduction to non-standard string literals can be found in this [blog post](https://web.archive.org/web/20170625222109/https://iaindunning.com/blog/julia-unicode.html). 
+You might like to use this exercise as an excuse to experiment with [non-standard string literals][nssl].
+A short introduction to non-standard string literals can be found in this [blog post][nssl-blog].
 
-You can extend your solution by adding the functionality described below.
+To pass the bonus tests, define a macro `rna_str` as explained in the links above, then your users could write code like this:
 
-## Bonus
-Implement a string literal that translates RNA strings as:
 ```julia
 rna"AUGUGU" == ["Methionine", "Cysteine"]
+
+rna"""
+AUGUUUUCUUAAAUG
+""" == ["Methionine", "Phenylalanine", "Serine"]
 ```
+
+[nssl]: https://docs.julialang.org/en/v1/manual/metaprogramming/#meta-non-standard-string-literals
+[nssl-blog]: https://web.archive.org/web/20170625222109/https://iaindunning.com/blog/julia-unicode.html