Adding "How to use" and files structure In Readme.md

**Is your feature request related to a problem? Please describe.**
There are lots of files present in our repo, we add a section that will be explaining the major files on which we have to work on.

**Describe the solution you'd like**
Add a section Usage which will contain the folder structure in this way :
(sample)

It will clear for all the contributor where to start from and what are the major files to be worked on.

**Describe alternatives you've considered**

**Approach to be followed (optional)**

**Additional context**