Update README to match new tutorial title

Author: lpozo

python-built-in-functions/README.md

@@ -1,3 +1,3 @@
-# Python's Built-in Functions: A Complete Exploration
+# Python Built-in Functions: A Complete Guide
 
-This folder provides the code examples for the Real Python tutorial [Python's Built-in Functions: A Complete Exploration](https://realpython.com/python-built-in-functions/).
+This folder provides the code examples for the Real Python tutorial [Python Built-in Functions: A Complete Guide](https://realpython.com/python-built-in-functions/).