update README.md

Author: pm990320

README.md

@@ -28,6 +28,25 @@ FIREBASE_AUTH = {
 }
 ```
 
+Alternatively, you can configure the Firebase credentials directly, like so:
+
+```
+FIREBASE_AUTH = {
+    'FIREBASE_CREDENTIALS': {
+        'type': "service_account",
+        'project_id': "",
+        'private_key_id': "",
+        'private_key': "",
+        'client_email': "",
+        'client_id': "",
+        'auth_uri': "https://accounts.google.com/o/oauth2/auth",
+        'token_uri': "https://accounts.google.com/o/oauth2/token",
+        'auth_provider_x509_cert_url': "https://www.googleapis.com/oauth2/v1/certs",
+        'client_x509_cert_url': ""
+    }
+}
+```
+
 ## Publishing
 
 `python setup.py sdist`