build: update node version, add nvmrc and contributor guide

Author: shaundon

.nvmrc

@@ -0,0 +1,2 @@
+14.18.2
+

.tool-versions

@@ -1 +1 @@
-nodejs 14.16.0
+nodejs 14.18.2

CONTRIBUTING.md

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+# Contribution guide
+
+## Setup
+
+1. Make sure you have the correct version of Node installed. If you use [`nvm`](https://github.com/nvm-sh/nvm), run `nvm use`. If you use [`asdf`](https://github.com/asdf-vm/asdf), run `asdf install`.
+1. Make sure you have `yarn ^1.0.0` installed: `npm install --global yarn`
+1. Install dependencies with `yarn`
+
+## Run locally
+
+Use `yarn dev` to run in dev mode.
+
+See `package.json` for other scripts that can be run (e.g. linters).
+
+## Committing code
+
+We use [commitlint](https://github.com/conventional-changelog/commitlint) to lint our commit messages. If your commit message doesn't fit this format, it'll be rejected by a pre-commit hook.