Update README.md (vercel#3784)

Detailed instructions for configuring authentication.

examples/with-firebase-authentication/README.md

@@ -23,10 +23,11 @@ cd with-firebase-authentication
 ```
 
 Set up firebase:
-- create a project
-- get your service account credentials and client credentials and set both in firebaseCredentials.js
-- set your firebase database url in server.js
-- on the firebase Authentication console, select Google as your provider
+- Create a project at the [Firebase console](https://console.firebase.google.com/).
+- Get your account credentials from the Firebase console at *settings>service accounts*, where you can click on *generate new private key* and download the credentials as a json file. It will contain keys such as `project_id`, `client_email` and `client id`. Now copy them into your project in the `credentials/server.js` file.
+- Get your authentication credentials  from the Firebase console under *authentication>users>web setup*. It will include keys like `apiKey`, `authDomain` and `databaseUrl` and it goes into your project in `credentials/client.js`.
+- Copy the `databaseUrl` key you got in the last step into `server.js` in the corresponding line.
+- Back at the Firebase web console, go to *authentication>signup method* and select *Google*.
 
 Install it and run: