Add a license to the repository

I recently came across your project Qiskit-QuantumComputing and I noticed that the repository github.com/JaimePSantos/Qiskit-QuantumComputing currently does not have a license specified.

Why Adding a License is Important?

As [GitHub documents](https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/licensing-a-repository)
>Public repositories on GitHub are often used to share open source software. For your repository to truly be open source, you'll need to license it so that others are free to use, change, and distribute the software.

Would be possible to add a valid license to this repository? Probably something really OpenSource such as the [Apache 2.0 license](https://www.apache.org/licenses/LICENSE-2.0) would fit really well.

Thanks!

Start by reading the linked GitHub licensing documentation and Apache 2.0 license page. Add a valid license to the repository, with Apache 2.0 suggested by the issue, and verify that the license is visible in the repository.

Written by the indexing model from the issue text.