Document the NorESM2.1 release

[TomasTorsvik]

I have created a noresm2.1 branch as a clone of the noresm2 branch.

Things to do before documentation release:

• [x] Remove specific topics related to CMIP6 (noresm2.0 version)
• [x] Add release notes
• [x] Notify that noresm2.1 is a technical release, and what this implies for use of the model
• [x] Add information about test runs for noresm2.1
• [x] Add information on longer test runs
• [x] Add information on build changes (AEROCOM)
• [x] Update main branch with info about the noresm2.1 branch
• [x] Write news item for noresm.org
• [ ] Update README.md file in NorESM repo for noresm2.1?

[gold2718]

Should we add all the information from the draft release notes?

[TomasTorsvik]

@gold2718 - yes, I think that's a good idea.

[TomasTorsvik]

I went ahead and created the noresm2.1 documentation on ReadTheDocs https://noresm-docs.readthedocs.io/en/noresm2.1/

It's the opposite of what we discussed yesterday, but I think it's useful to see that the documentation builds and see how it turns out.

[gold2718]

I'm not following (or maybe misunderstood what we discussed yesterday), what is different?

[TomasTorsvik]

@gold2718 - Yesterday we (or maybe I, specifically) said that noresm2.1 documentation could wait until after the noresm2.1 version was released, but now the noresm2.1 documentation page is already available on Read The Docs. We will of course update it as we go along, so it's not a final version.

[mvertens]

@TomasTorsvik - thanks for clarifying and for doing this. Its helpful to already have this in place.

[gold2718]

Finished by #30