Solve the following problem with Lean 4 code and explanatory comments:

```lean4
import Mathlib


theorem demo (n : ℕ) : n + 0 = n := by sorry
```

Replace every sorry statement with an appropriate proof. Provide a complete solution in the lean4 code block, annotated with Lean 4 compiler feedback blocks in the form `/- <feedback> ... </feedback> -/` at the appropriate locations.