Review: deploy documentation to ReadTheDocs

[cthoyt]

As a follow-up to #4, the documentation should be deployed to ReadTheDocs. This has the advantage that users don't have to build the documentation themselves, and that it automatically stays up-to-date with changes in the code.

[cthoyt]

This was not done.

[r-costa]

Thank you for highlighting this aspect. We now provide the ReadTheDocs https://sbml2hyb.readthedocs.io/en/latest/# .