Add a simple CONTRIBUTING.md

CONTRIBUTING.md

@@ -0,0 +1,21 @@
+# Contributing
+
+## Installing dependencies
+
+```bash
+yarn
+```
+
+`npm` doesn't install the correct dependencies for `eslint` so we use `yarn`.
+
+## Regenerating dist/index.js
+
+```bash
+yarn run package
+```
+
+It is recommended to add this as a `git` `pre-commit` hook:
+
+```bash
+cp pre-commit .git/hooks/pre-commit
+```