Add dependency install section in pyproject.toml

[bobleesj]

As of now, the cookiecuttered projects do not install the dependencies because pyproject.toml has no section that provides a pathway for the files to install:

Issue on GitHub

Tieqiong made a PR here to fix the issue in diffpy.structure:

Pull Request on GitHub

Once this solution is implemented, we shall update the current cookiecutter pyproject.toml and all other cookiecuttered projects.