Update README.md

Author: mpociot

README.md

@@ -16,6 +16,11 @@ Mailbox::from('{username}@gmail.com', function (InboundEmail $email, $username)
 });
 ```
 
+[![https://phppackagedevelopment.com](https://beyondco.de/courses/phppd.jpg)](https://phppackagedevelopment.com)
+
+If you want to learn how to create reusable PHP packages yourself, take a look at my upcoming [PHP Package Development](https://phppackagedevelopment.com) video course.
+
+
 ## Installation
 
 You can install the package via composer: