Add implementation of Depth-First Search

[eivindlie]

Add an example implementation of the Depth-First Search algorithm in SearchingAlgorithms/GraphSearch/depth_first_search.py

[Neverbolt]

Will do if it is not already done

[kaushikthedeveloper]

Hello.

Check out GeeksforGeeks Python project. It contains scripts for many Algorithms and is continuously growing. The above requested code too can be found there.