Move Quickstart instructions to `post_gen_project.py`

[sobrinojulian]

For example:

def main():
    set_python_version()
    # Initialise git repo
    os.system('git init')
    # Install dependencies
    os.system('pipenv install --dev')
    # Setup pre-commit and pre-push hooks
    os.system('pipenv run pre-commit install -t pre-commit')
    os.system('pipenv run pre-commit install -t pre-push')
    print(SUCCESS + "Project successfully initialized" + TERMINATOR)