NEX methodology section

[Jakidxav]

This will be particularly useful in explaining more about how we calculate warming levels years, which models are being used in NEX input data, and which years are being used for each model.

The best place for this documentation may not be on this site, though. It would be better to include it on the README or in the methodologies site as it will be long.

[Jakidxav]

Currently, we link to the Woodwell Risk methodologies site in the Climate risk section's dropdown text in the sidebar. This leads to the page with the full report and the GitHub repository for the warming levels work. However, it might also be helpful to include the specific (much smaller) table that we used to create NEX-based layers on this site.