Add back-to-top scroll up button in readme file

[T-Fathima]

I would like to propose to add a button at the bottom of the readme file. While clicking, it returns to the top of the page for easier navigations through lengthy readme files and better user experience.

@tanishaness I would like to work on it. Please assign it to me.

[veepanshu-kasana]

@tanishaness I want to contribute to this project on this particular issue. Please assign it to me!