Add Python Data Science Handbook link

### What I did
Added a new free Python learning resource to the Python section in the free courses list.

### Resource added
- Python Data Science Handbook (full content): https://jakevdp.github.io/PythonDataScienceHandbook/

### Why
This book is a high-quality, complete, and freely accessible resource that helps learners understand data science using Python. It benefits beginners as well as intermediate developers.

### Notes
If anything needs to be updated, I will be happy to make the changes 😊

Author: gellikeerthi

courses/free-courses-en.md

@@ -1656,6 +1656,7 @@
 * [Python: Visually Explained](https://www.youtube.com/playlist?list=PL8HmoRTjTSlHFhqRC_2iavGUOVnUdfAyl) - Visually Explained
 * [The Python Tutorial](https://docs.python.org/3/tutorial/)
 * [Using Python for Research](https://www.edx.org/course/using-python-for-research) (edX Harvard)
+* [Python Data Science Handbook (full content)](https://jakevdp.github.io/PythonDataScienceHandbook/)
 
 
 #### Django