Mention that start_url needs to be "." for client side routing

* Change template manifest start_url to dot to make it react-router friendly

* Revert "Change template manifest start_url to dot to make it react-router friendly"

This reverts commit 02f53e81.

* Add a note about PWA manifest and client-side routing

packages/react-scripts/template/README.md

@@ -1836,6 +1836,12 @@ service worker navigation routing can be configured or disabled by
 and [`navigateFallbackWhitelist`](https://github.com/GoogleChrome/sw-precache#navigatefallbackwhitelist-arrayregexp)
 options of the `SWPreachePlugin` [configuration](../config/webpack.config.prod.js).
 
+When users install your app to the homescreen of their device the default configuration will make a shortcut to `/index.html`. This may not work for client-side routers which expect the app to be served from `/`. Edit the web app manifest at [`public/manifest.json`](public/manifest.json) and change `start_url` to match the required URL scheme, for example:
+
+```js
+  "start_url": ".",
+```
+
 ### Building for Relative Paths
 
 By default, Create React App produces a build assuming your app is hosted at the server root.<br>