Update sample .env

.env.production.sample

@@ -15,6 +15,7 @@ LOCAL_HTTPS=true
 # Generate each with the `rake secret` task (`docker-compose run --rm web rake secret` if you use docker compose)
 PAPERCLIP_SECRET=
 SECRET_KEY_BASE=
+OTP_SECRET=
 
 # Registrations
 # Single user mode will disable registrations and redirect frontpage to the first profile
@@ -41,3 +42,6 @@ SMTP_FROM_ADDRESS=notifications@example.com
 
 # Optional alias for S3 if you want to use Cloudfront or Cloudflare in front
 # S3_CLOUDFRONT_HOST=
+
+# Optional Firebase Cloud Messaging API key
+FCM_API_KEY=