Context around TypeScript

[wycats]

The guides could use an early (optional) introduction to TypeScript and link to more resources.

Probably a link to Tom's blog post and some of its content would be appropriate.

We should probably not fully outsource the docs; the details of how to use TS with Glimmer don't require learning all of TypeScript, and a guide focused on what you need to be quickly productive in using Glimmer with TypeScript (focused on examples you'd really write) is important to avoid users feeling overwhelmed.

We should also likely give people advice about using TypeScript with VSCode if they don't already have a strong editor preference.