Add a tutorial on rotating equivariants

[frostedoyster]

As in the title, using Wigner D-matrices in their real form

[frostedoyster]

@ceriottm @DavideTisi Wasn't there supposed to be a preview?

[Luthaf]

There is an artifact associated with the Documentation workflow, I don't think this repo is setup to automatically add a link to the artifact in the first PR comment.

[Luthaf]

oh, it is setup, but HttpError: You have exceeded a secondary rate limit. Please wait a few minutes before you try again. https://github.com/lab-cosmo/atomistic-cookbook/actions/runs/12258187390

[github-actions]

Here is the build version of the cookbook in this pull request: documentation.zip, you can view it locally by unzipping documentation.zip and open the index.html with your favorite browser.