Typo corrections and suggested sentence re-structuring [JOSS REVIEW]

I noticed a couple of mistakes that are easily fixable and rather than outlining them to you, I just thought it was easier to do them myself and make a merge request. These are just typo corrections and suggested sentence re-structuring in the IPCC repo readme, documentation and JOSS paper. Feel free to adjust anything if needed.

Once merged with your joss branch, please make sure that the changes to the readme and documentation is also merged over to the main branch.

The rest of my suggested changes will be here.