Update design.md of each concept exercise to include analyzer comments

[sanderploegsma]

The .meta/design.md file of each concept exercise should contain a section describing what feedback the analyzer should provide and when. This is a prerequisite for implementing the analyzer for each of these exercises.

The section should clearly describe what should be checked by the analyzer, what feedback should be given to the student and the type of each comment (essential, actionable, informative or celebratory, see the documentation).

Here is a good example of what it might look like: https://github.com/exercism/javascript/blob/main/exercises/concept/mixed-juices/.meta/design.md

When writing this section for a specific concept exercise, make sure to keep the following guidelines in mind: https://exercism.org/docs/building/tooling/analyzers/comments

[sanderploegsma]

Split up into separate issues