Add development docs

docs/development.md

@@ -0,0 +1,27 @@
+# Development
+
+## How this action works
+
+This action works by evaluating the user input as the body of an asynchronous
+JavaScript function. See [main.ts](/src/main.ts) for details.
+
+## Building
+
+Before the action can be used, it needs to be compiled to JavaScript:
+
+```shell
+bash> npm run build
+```
+
+It also has a pre-commit hook configured via
+[husky](https://www.npmjs.com/package/husky) that should run the build script
+before each commit.
+
+## Releasing
+
+Releases are done manually, for now:
+
+1. Ensure that the build is up to date with `npm run build`.
+1. Bump the [package.json](/package.json#L3) and [package-lock.json](/package-lock.json#L3) version numbers and commit them.
+1. Update documentation (including updated version numbers).
+1. Tag master with the new version number and create a GitHub release.