(docs) add Realtime Database setup

Author: antoine92190

README.md

@@ -510,6 +510,7 @@ You can find the source code to implement a full featured chat app using Firebas
 <br>
 To test it using your own Firebase project:
 
+- Setup Cloud Firestore (to store users and rooms) and Realtime Database (to store users online status)
 - Clone this repository: `git clone https://github.com/antoine92190/vue-advanced-chat.git`
 - Inside `demo/src/firestore/index.js` file, replace the line `const config = ...` by your own Firebase config
 - Go inside `demo` folder and run `npm run serve`