update overview link

Author: amitkaps

README.md

@@ -6,7 +6,7 @@ This is a repository for the data science workshop in Python to be conducted by
 - [Installation](Installation.md) - To get yourself ready for the workshop.
 - [Schedule](schedule.md) - The broad schedule for the workshop
 - [Introduction](introduction.md) - The overall introduction to the workshop.
-- [Overview](Overview.md) - The overview presentation for the workshop.
+- [Overview](overview.md) - The overview presentation for the workshop.
 - [Intro to Data Structures in Python](IntroPython.ipynb) - Get started with Python.
 
 Case Studies