Format docstrings and add sphinx docs

[Cmurilochem]

This PR adresses #46.

Sections to add in the documentation

• [x] Introduction
• [x] Installation instructions including overview of qc2 workflow
• [x] General consideration on how to use and develop new qc2-ASE calculators
• [x] Instructions of how to instantiate qc2Data class and use its methods
• [x] Tutorials and examples
  • [x] Jupyter notebook 1: Qiskit VQE example
  • [x] Jupyter notebook 2: PennyLane VQE example
  • [x] Jupyter notebook 3: VQE with IBMQ Qiskit runtime
  • [x] Added provisory logo

Instructions on how to visualise the final HTML documentation

Since we our repo is still Private, we are not yet able to deploy the documentation directly from the CI/CD to ReadTheDocs or Github pages.

As a provisory solution to visualise the final html doc file, proceed as follows:

1. First, make sure that you have installed qc2 using the dev option, e.g.,:

   python3 -m pip install -e .[dev,pennylane]

   This will install all functionalities of sphinx.

2. Go to the docs directory and compile the documentation via the command:

   make html

3. Finally, open the generated _build/html/index.html file using your browser.