Clarify comments in .env.example

Updated comments in .env.example for clarity on REDIRECT_URI and PORT.

Author: JustinaPetr

samples/app-client-starter-app/.env.example

@@ -2,10 +2,10 @@
 BUFFER_CLIENT_ID=your_client_id
 BUFFER_CLIENT_SECRET=your_client_secret
 
-# Must match what you registered, character for character
+# Can be changed to your own REDIRECT_URI. Must match what you registered, character for character
 REDIRECT_URI=https://localhost:3000/callback
 
-#PORT your app is running on locally.
+#PORT your app is running on locally. Can be changed to match the details in your custom REDIRECT_URI.
 PORT=3000
 
 # Encrypts the session cookie; 32 characters minimum. Leave it empty locally and