update installation instructions

Author: rwieruch

README.md

@@ -39,6 +39,6 @@
 
 ### Use your own Firebase Credentials
 
-* visit https://firebase.google.com/ and create a Firebase App
-* copy and paste your Credentials from your Firebase App into src/firebase/firebase.js
-* activate Email/Password Sign-In Method in your Firebase App
+* visit https://firebase.google.com and create a Firebase App
+* copy and paste your Credentials from your Firebase App into *src/components/Firebase/firebase.js* file or in .env file
+* activate Email/Password, Google, Facebook and Twitter Sign-In Methods for your Firebase App