Update .env.example

Update description for ANDROID_APP_KEYS

Author: robinske

passkeys-backend/.env.example

@@ -3,7 +3,7 @@
 # required: true
 API_URL=https://comms.twilio.com/preview
 
-# description: The domain of the adroid identity provider
+# description: [Optional] Comma separated domains for Android application
 # format: list(text)
 # required: false
 ANDROID_APP_KEYS=