Remove MyBinder HTTPS remotes URL and update docs URL

Since SKD v292 the remote in JUICE metakernels are pointing to the HTTPS endpoint and no longer the FTP. This fixed the security issue with MyBinder globally.

We also provide a new canonical entry point for the documentation (moon-coverage#27).

• Remove MyBinder alternative remote URL
• Replace https://moon-coverage.readthedocs.io by https://moon-coverage.univ-nantes.fr