Add testing docs

README.md

@@ -39,4 +39,15 @@ This project was created using:
 4. Build storybook.
     ```
     $ yarn build-storybook
+    ```
+
+### Testing
+
+Use Storybooks [built-in test-runner](https://storybook.js.org/docs/react/writing-tests/test-runner):
+
+1. Run a local instance of storybook in one process.
+
+2. Invoke the test runner in another. Note: depending on the power of you machine, you may have to reduce concurrent workers to avoid test timeout failures. Use `--maxWorkers=2` to limit the workers to two.
+    ```
+    $ yarn test-storybook
     ```