feat: added article on Branded Types

## PR Checklist - [x] Addresses an existing open issue: fixes #133 - [x] That issue was marked as [accepting prs](https://github.com/LearningTypeScript/site/issues?q=is%3Aopen+is%3Aissue+label%3A%22accepting+prs%22) - [x] Steps in [CONTRIBUTING.md](https://github.com/LearningTypeScript/site/blob/main/.github/CONTRIBUTING.md) were taken ## Overview ~Got through about half of it so far.~ ✅ This is complete. Once typescript-eslint's `no-floating-promises` augmentations are shipped, I'll clean this up and put it in review. ~Tentatively early-mid-June or so.~ early-August it is! The only blocker to publish is that I'd like `ts-brand` to be published with its latest `make` additions: https://github.com/kourge/ts-brand/issues/11.