minor: Fix Functional API guide (keras-team#20694)

Add an empty line so the list is rendered as a list, not as a single line of text

guides/functional_api.py

@@ -179,6 +179,7 @@
 from this file, even if the code that built the model is no longer available.
 
 This saved file includes the:
+
 - model architecture
 - model weight values (that were learned during training)
 - model training config, if any (as passed to `compile()`)