Add BSD-3-Clause license file to repository

[Jorgelmh]

Description

Resolves #64

Add BSD-3-Clause license file to repository to prepare for open-sourcing the package.

How Has This Been Tested?

• No tests.

Developer Checklist (before requesting PR review)

• My code follows the style guidelines of this project
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules

I have:

• commented my code, particularly in hard-to-understand areas
• performed a self-review of my own code
• not committed unnecessary formatting changes, thereby occluding the actual changes (e.g. change of tab spacing, eol, etc.)
• made corresponding changes to the documentation
• added change to CHANGELOG.md
• added tests that prove my fix is effective or that my feature works (for core features)

Reviewer checklist

I have:

• performed a self-review of my own code have performed a review of the code
• tested that the software still works as expected
• checked updates to documentation
• checked that the CHANGELOG is updated

[Jorgelmh]

PR 61 introduced LICENSE file so closing this PR