Arrays concept docs

[glennj]

• don't use dot-bracket syntax
• fix some erroneous list syntax in concept exercise introduction

[glennj]

Is there a particular reason why the concept exercises don't use templates for their introductions?

[glennj]

I never took the time to convert them 🤷 Would be useful.

I can follow up

[ErikSchierboom]

That would be great! (if you're keen on more work, C# could use the same PR 😉 )