Add backend/.env.example to help new contributors

[yogitha-star]

This adds a sample environment file backend/.env.example with placeholders
and updates README with instructions on how to use it.

[yogitha-star]

Hi @Alen983,

I have created the backend/.env.example file with placeholder variables and updated
the README with setup instructions for new contributors. (#18)

[Alen983]

Good work on the .env.example file. It's clear and well-organized.

Two small suggestions:

1. Update DATABASE_URL to match the default from config.py:
   DATABASE_URL=sqlite:///./data/employee_portal.db

2.Remove PORT and DEBUG — they're not used in the config, so removing them avoids confusion.

Otherwise, looks good. The README instructions are clear and helpful.

[yogitha-star]

Hi @Alen983,

I’ve updated the DATABASE_URL to match config.py and removed the unused environment variables as suggested.

Please let me know if everything looks good now. Thanks

[yogitha-star]

Hi @Alen983

Just a gentle follow-up to check if the latest changes look good now.
Happy to make any further updates if needed.

Thanks