Fix formatting `whats-new.rst` for doc-building

[JoranAngevaare]

Fix documentation building

This is probably more related to one sub-packages of sphinx that is actually causing the issue, but I think this should do the trick to get the documentation building back up.

New page is on: https://cmip6-preprocessing--366.org.readthedocs.build/en/366/whats-new.html

1. First try (6474e49) did look to kind of bad looking information:

2. Second try (de712ae) also yielded something horrible

3. The third try (fdbe8c3) actually fixes the issue

4. The fourth commit fixes the strange rst syntax which no one remembers ef138c9. Now the hyperlinks to the authors work.

5. Commit nr. 5/6 adds this PR to the whats-new.rst