Update intro_to_keras_for_engineers.py

Corrected grammar in the introduction

guides/intro_to_keras_for_engineers.py

@@ -9,7 +9,7 @@
 """
 ## Introduction
 
-Keras 3 is a deep learning framework
+Keras 3 is a deep learning framework that
 works with TensorFlow, JAX, and PyTorch interchangeably.
 This notebook will walk you through key Keras 3 workflows.