lasagna: describe Analyzer feedback in `.meta/design.md`

[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 analyzer for the lasagna exercise has already been implemented, so the goal of this issue is to just make sure the existing analyzer feedback is also described in the exercise's .meta/design.md.

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