Merge pull request #432 from storybookjs/docs/add-pnp-remark

Docs: Add remark regarding pnp support

Author: yannbf

README.md

@@ -47,6 +47,7 @@ Storybook test runner turns all of your stories into executable tests.
   - [DOM snapshot (HTML)](#dom-snapshot-html)
   - [Image snapshot](#image-snapshot)
 - [Troubleshooting](#troubleshooting)
+  - [Yarn PnP (Plug n' Play) support](#yarn-pnp-plug-n-play-support)
   - [React Native support](#react-native-support)
   - [The error output in the CLI is too short](#the-error-output-in-the-cli-is-too-short)
   - [The test runner seems flaky and keeps timing out](#the-test-runner-seems-flaky-and-keeps-timing-out)
@@ -983,6 +984,19 @@ export default config;
 
 ## Troubleshooting
 
+#### Yarn PnP (Plug n' Play) support
+
+The Storybook test-runner relies on a library called [jest-playwright-preset](https://github.com/playwright-community/jest-playwright), of which does not seem to support PnP. As a result, the test-runner won't work out of the box with PnP, and you might have the following error:
+
+```
+PlaywrightError: jest-playwright-preset: Cannot find playwright package to use chromium
+```
+
+If that is the case, there are two potential solutions:
+
+1. Install `playwright` as a direct dependency. You might need to run `yarn playwright install` after that, so you install Playwright's browser binaries.
+2. Switch your package manager's linker mode to `node-modules`.
+
 #### React Native support
 
 The test-runner is web based and therefore won't work with `@storybook/react-native` directly. However, if you use the [React Native Web Storybook Addon](https://storybook.js.org/addons/%2540storybook/addon-react-native-web), you can run the test-runner against the web-based Storybook generated with that addon. In that case, things would work the same way.