Rework rna-transcription documentation (#2251)

This PR is part of our project of making our Practice Exercises
more consistent and human. For more context please see the
following forum-thread:
https://forum.exercism.org/t/new-project-making-practice-exercises-more-consistent-and-human-across-exercism/3943

The main change is to frame the exercise within the context of story.

Author: kytrinyx

exercises/rna-transcription/description.md renamed to exercises/rna-transcription/instructions.md

@@ -1,6 +1,6 @@
-# Description
+# Instructions
 
-Given a DNA strand, return its RNA complement (per RNA transcription).
+Your task is determine the RNA complement of a given DNA sequence.
 
 Both DNA and RNA strands are a sequence of nucleotides.
 
@@ -14,3 +14,7 @@ Given a DNA strand, its transcribed RNA strand is formed by replacing each nucle
 - `C` -> `G`
 - `T` -> `A`
 - `A` -> `U`
+
+~~~~exercism/note
+If you want to look at how the inputs and outputs are structured, take a look at the examples in the test suite.
+~~~~

exercises/rna-transcription/introduction.md

@@ -0,0 +1,16 @@
+# Introduction
+
+You work for a bioengineering company that specializes in developing therapeutic solutions.
+
+Your team has just been given a new project to develop a targeted therapy for a rare type of cancer.
+
+~~~~exercism/note
+It's all very complicated, but the basic idea is that sometimes people's bodies produce too much of a given protein.
+That can cause all sorts of havoc.
+
+But if you can create a very specific molecule (called a micro-RNA), it can prevent the protein from being produced.
+
+This technique is called [RNA Interference][rnai].
+
+[rnai]: https://admin.acceleratingscience.com/ask-a-scientist/what-is-rnai/
+~~~~