Edit tutorial by @srush.

- Rebase on top of main branch.
  - Some code snippets do not yet compile due to syntax changes.
    This should be straightforward to fix.
- Stylistic edits: use consistent terminology and voice.
  - Remove some second person "you" references.
  - Use consistent Dex and programming languages terminology and spellings.
   - Consistently use "array" everywhere: no mentions of "table"
   - Consistently use "`for` comprehension"
  - Consistent formatting, punctuation, heading casing (first word uppercase).