feat: add explanations

[leje512]

If someone doesn't remember any syntax, or just wants to take a look at a concept, to see if it makes sense in the current exercise, the concepts should be explained somewhere. This should probably happen in the mainsite. There could be a dictionary with toggle concerning elements used in the exercise, there could also just be a search function or similar, that shows some explanation for how it works.

TODOS:

• work out some ideas on how this should be presented
• wireframes
• get a second opinion!
• implement favored version:)