Added Counting sort documentation

[muskan467]

Description

Created Counting sort documentation that gives a proper explanation with examples of how a Counting sort works with its Algo and code implemented in C++.

• [x] Swoc Participant

Fixes: #55

Type of change

Added Counting Sort Documentation in Algorithms folder.

• [x] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)

Checklist:

• [x] I have taken help from some online resources
• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings

[muskan467]

@Sulagna-Dutta-Roy Please merge it