docs: describes release process.

docs/release.md

@@ -0,0 +1,38 @@
+# Internal release documentation
+
+This document is for project maintainers and contributors. It describes the steps to release a new version of the project.
+
+## Prerequisites
+
+- [Node.js](https://nodejs.org) installed
+- [npm](https://www.npmjs.com/get-npm) installed
+
+## Steps
+
+1. Switch to the `main` branch.
+2. Run the tests to ensure everything is working as expected.
+3. Follow the steps below to release the package.
+
+### Automated release
+
+Use the release script to publish a new version of the package to npm.
+
+```bash
+cd scripts
+./prep-release.sh <release type>
+```
+
+This script will:
+
+1. Update the version number in `package.json` and `package-lock.json` using `npm version <version number>` in line with [Semantic Versioning](https://semver.org/).
+2. Create a new git tag.
+
+You must then push the changes to the repository with `git push origin main --tags`. The GitHub Actions workflow will automatically publish the package to npm if the tests pass.
+
+### Manual release
+
+If you need to release manually, follow these steps:
+
+1. Update the version number in `package.json` and `package-lock.json` using `npm version <version number>` in line with [Semantic Versioning](https://semver.org/). This will also create a new git tag.
+2. Push the changes to the repository with `git push origin main --tags`. 
+3. The GitHub Actions workflow will automatically publish the package to npm if the tests pass.