Number of Islands _ DFS.cpp

[RuchNas-Pottah]

This contains an accepted solution to the problem 'Number of Islands' on LeetCode, done with the help of the Depth-First-Search algorithm.

Fixes issue: Added a concise and easily understandable code for the problem.

Changes: Made the code understandable, used DFS, and followed a proper breakdown of functions.

[RuchNas-Pottah]

Sir, I have updated the code with an explanation of the sample input.

[RuchNas-Pottah]

Include the complete code with main() function which one can run on terminal.

Sir, I have updated the complete code with the main() function that runs in the terminal.

[RuchNas-Pottah]

@AdiChat Sir please review my updated pull request