text: Title: "ploomber install" should add venv directory to .gitignore
  Body: (Also create .gitignore if it doesn't exist)
  
  `pip install` automates dependency installation and creating lock files. When using pip, the command first creates a venv in the current directory, such directory must be added to .gitignore to prevent it from being committed.
  
  https://github.com/ploomber/ploomber/blob/ac915ea998f4da0177204f2189f8f608f3404fc6/src/ploomber/cli/install.py#L83