refactor: Add .env.example file && Wrong path mentioned in readme

Proposed Refactor

There should be .env.example file in both front-end and backend files , it will help a lot for contributors to setup it locally well
"VITE_API_URL=http://localhost:5000" URL path mentioned in readme file under the getting started section , it's an wrong path it should be "VITE_API_URL=http://localhost:5000/api" , it was causing an issue connecting frontend to backend while setting up locally

If it possible then add hacktoberfest label here since hactoberfest is going on , it would be better us !

I have fixed this issue #158 and also i have raised an PR for another issue #156 , would you please look to once