Add documentation for credential option when upgrade larval 5.2.0

cjyclaire · cjyclaire · commit acca382743f6 · 2016-07-11T22:24:07.000-07:00
diff --git a/README.md b/README.md
@@ -89,6 +89,9 @@ return [
 ];
 ```
 
+Referring Laravel 5.2.0 [Upgrade guide](https://laravel.com/docs/5.2/upgrade#upgrade-5.2.0), you must using config 
+file instead of environment variable option if using php artisan `config:cache`.
+
 Learn more about [configuring the SDK](http://docs.aws.amazon.com/aws-sdk-php/v3/guide/guide/configuration.html) on
 the SDK's User Guide.
 
