Unclear test/instructions for rna translation exercise

[WeeDom]

exercises/rna-transcription/description.md

Instructions and test could be improved for this exercise, and possibly a review of the instructions and tests for the same exercise where it exists on other tracks.- but this is just a placeholder issue which I'll pad out at not stupid-o-clock on a work night. Refer to slack for initial details:

https://exercism.io/mentor/solutions/bec7418c170d4d0393708f3bed615129

https://exercism-team.slack.com/archives/CASLGCCSZ/p1619386312066700