📝 Add documentation badge and stabilize banner image link (#12)

## Description

This pull request adds a documentation build badge to the project for
better visibility of the documentation status. Additionally, it updates
the banner to point to a stable image link, ensuring the banner displays
correctly in the rendered PyPI README.

## Checklist:

- [x] The pull request only contains commits that are related to it.
- [x] I have added appropriate tests and documentation.
- [x] I have made sure that all CI jobs on GitHub pass.
- [x] The pull request introduces no new warnings and follows the
project's style

Author: burgholzer

README.md

@@ -3,9 +3,12 @@
 [![License: MIT](https://img.shields.io/badge/license-MIT-blue.svg?style=flat-square)](https://opensource.org/licenses/MIT)
 [![CI](https://img.shields.io/github/actions/workflow/status/cda-tum/mqt-yaqs/ci.yml?branch=main&style=flat-square&logo=github&label=ci)](https://github.com/cda-tum/mqt-yaqs/actions/workflows/ci.yml)
 [![CD](https://img.shields.io/github/actions/workflow/status/cda-tum/mqt-yaqs/cd.yml?style=flat-square&logo=github&label=cd)](https://github.com/cda-tum/mqt-yaqs/actions/workflows/cd.yml)
+[![Documentation](https://img.shields.io/readthedocs/mqt-yaqs?logo=readthedocs&style=flat-square)](https://mqt.readthedocs.io/projects/yaqs)
 [![codecov](https://img.shields.io/codecov/c/github/cda-tum/mqt-yaqs?style=flat-square&logo=codecov)](https://codecov.io/gh/cda-tum/mqt-yaqs)
 
-![Banner](images/banner.jpeg)
+<picture>
+<img src="https://raw.githubusercontent.com/cda-tum/mqt-yaqs/main/images/banner.jpeg" width="95%" alt="MQT YAQS Banner">
+</picture>
 
 # MQT YAQS: A Tool for Simulating Open Quantum Systems, Noisy Quantum Circuits, and Realistic Quantum Hardware