update readme with firebase functions setup (#848)

CONTRIBUTING.md

@@ -64,16 +64,24 @@ This will setup your project along with firebase emulator in a docker environmen
     - This nickname is an internal, convenience identifier and is only visible to you in the Firebase console.
     - Click Register app.
 5. Copy the firebase configuration.
-6. Paste the configuration `.env` file. **(this will be found in the project settings section of firebase cloud)**
-7. You can find your `<FIREBASE_DATABASE_URL>` in the Realtime Database section of the Firebase console. Depending on the location of the database, the database URL  will be in one of the following forms:
+6. Follow the below steps to setup firebase functions
+    - Go to functions directory (`cd functions`) and install dependencies (`npm install`)
+    - Create a folder `private` inside functions directory
+    - Then you have to generate a private key file for your service account. Follow the below steps to get private key:
+      1. In the Firebase console, open Settings > Service Accounts.
+      2. Click Generate New Private Key, then confirm by clicking Generate Key.
+      3. Securely store the JSON file containing the key and rename it to `cl-dev-pk.json`
+      4. Move the `cl-dev-pk.json` to `Codelabz/functions/private`
+7. Paste the configuration `.env` file. **(this will be found in the project settings section of firebase cloud)**
+8. You can find your `<FIREBASE_DATABASE_URL>` in the Realtime Database section of the Firebase console. Depending on the location of the database, the database URL  will be in one of the following forms:
     - `https://DATABASE_NAME.firebaseio.com` **(for databases in us-central1)**
     - `https://DATABASE_NAME.REGION.firebasedatabase.app`**(for databases in all other locations)**
-8. You can get your `<FIREBASE_VAPID_KEY>` from Cloud-Messaging tab
+9. You can get your `<FIREBASE_VAPID_KEY>` from Cloud-Messaging tab
     - navigate to the setting of your project Open the Cloud Messaging tab.
     - scroll to the Web configuration section.
     - In the Web Push certificates tab, click Generate Key Pair. The console displays a notice that the key pair was generated. You get your Vapid key form there.
-9. As you're using emulator, set `<USE_EMULATOR>` to "true" 
-10. You can get your `<CYPRESS_PROJECT_ID>` as cypress project id from [cypress cloud](https://cloud.cypress.io)
+10. As you're using emulator, set `<USE_EMULATOR>` to "true" 
+11. You can get your `<CYPRESS_PROJECT_ID>` as cypress project id from [cypress cloud](https://cloud.cypress.io)
 
 You should fill in these values in their relevant fields in the `.env` file.