Start writing changelog entries

[pokey]

• [ ] Add a page to contributor docs about how to do it
• [ ] add checkbox to PR template
• [ ] Add an example on one of our PRs

Could eventually be used to automate part of https://github.com/cursorless-dev/cursorless/issues/491

For example, we might create a file

changelog/2023-08-expanded-talon-api.md:

---
tags: [lang-talon, scope-namedFunction, enhancement]
---

- Expand the Talon API

[auscompgeek]

Depending on how much we want multiple tags, there's tools like towncrier for this sort of thing