add code of conduct

[S-ishita]

Hi there! I recommend adding a CODE_OF_CONDUCT.md file to your repository. This file would serve as a guide for potential contributors, providing them with a clear set of expectations, guidelines, and behavior standards for participating in your project. It plays an essential role in creating a welcoming and inclusive environment for everyone involved.

I would like to work on this issue. Please assign it to me under GSSoC'23.

Thank you!