Add devcontainer config

[spenserblack]

See #22 for previous discussion

This allows potential contributors to work in a GitHub Codespace with minimal setup on their end. They can start a codespace by clicking "Code" in the top-right of the repository's page, switching from the "Local" to the "Codespaces" tab, and then create a new codespace.

The contributors devcontainer will have Node, Typescript, and pnpm pre-installed. Once the container is created, nvm will install the appropriate Node version, and then pnpm i will be executed. Basically, the postCreateCommand will run the project setup in CONTRIBUTING.md for them.

Then, for the sake of convenience, the postAttachCommand will build the project in watch mode.

---

There are a few useless commits in this PR, so you'd probably want to squash-merge :laughing:

[spenserblack]

Side note: any interest in using an .editorconfig file?

[privatenumber]

Thanks for the PR, but I'm not currently interested in adding specific support for GitHub Codespaces/Devcontainers. Maybe in the future when I see more people using it.

[spenserblack]

adding specific support for GitHub Codespaces/Devcontainers

Just to clarify, this PR isn't for adding aicommits to a devcontainer. This allows maintainers or outside contributors to set up a devcontainer to develop aicommits. Otherwise users who don't have a dev environment set up locally and would prefer using Codespaces (like me 🙂) might diverge from the recommended contributing guide. The default codespace container will run npm install, for example. Just double-checking since "adding support" could have more than one meaning 🙂

Side note: you might want to add package-lock.json and yarn.lock to your gitignore to avoid PRs that accidentally commit those other lock files.

[privatenumber]

Yeah, I understand. Thanks for clarifying. I don't think the need for it has come up so far (e.g. this PR hasn't gotten traction like other PRs, and no one has submitted the wrong lock file.).