Write a documentation about URL Shortner

[utkarsh006]

• Write an article about how the URL Shortner works in the background.
• This article would be on Low Level System Design.
• Do consider this issue under hacktoberfest.

[origranot]

Go for it. 👍

[utkarsh006]

@origranot Kindly give this issue a label as "hacktoberfest"

[origranot]

Yes, I will label the PR 👍