Fixed link to manifest.json file (facebook#5704)

Author: m4jing

docusaurus/docs/making-a-progressive-web-app.md

@@ -93,11 +93,11 @@ following into account:
 ## Progressive Web App Metadata
 
 The default configuration includes a web app manifest located at
-[`public/manifest.json`](public/manifest.json), that you can customize with
+[`public/manifest.json`](https://github.com/facebook/create-react-app/blob/master/packages/react-scripts/template/public/manifest.json), that you can customize with
 details specific to your web application.
 
 When a user adds a web app to their homescreen using Chrome or Firefox on
-Android, the metadata in [`manifest.json`](public/manifest.json) determines what
+Android, the metadata in [`manifest.json`](https://github.com/facebook/create-react-app/blob/master/packages/react-scripts/template/public/manifest.json) determines what
 icons, names, and branding colors to use when the web app is displayed.
 [The Web App Manifest guide](https://developers.google.com/web/fundamentals/engage-and-retain/web-app-manifest/)
 provides more context about what each field means, and how your customizations