Update documentation to reflect larger remit of CSET

[Sylviabohnenstengel]

fixes #1823

Contribution checklist

Aim to have all relevant checks ticked off before merging. See the developer's guide for more detail.

• Documentation has been updated to reflect change.
• New code has tests, and affected old tests have been updated.
• All tests and CI checks pass.
• Ensured the pull request title is descriptive.
• Conda lock files have been updated if dependencies have changed.
• Attributed any Generative AI, such as GitHub Copilot, used in this PR.
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[github-actions]

[ukmo-huw-lewis]

In general, think these are looking like good changes.

Review has got me thinking further on some aspects, maybe in particular greater use of bullets to aid readability, and some suggested/requested changes to phrasing and emphasis that I hope worth considering before we make these changes.

Note also comment on value of consistency with top-level GitHub pages.

Finally, given the shift to Community Seamless Evaluation Toolkit, I have had in view the value of setting out what these words mean - I think each is powerful and usefully explain some of the 'philosophy' and what to expect from CSET. Can we add this narrative somewhere? A starter for 10 offered below (have a go at making these shorter/impactful etc):

Community: Software developed for and by a wide network of model development and evaluation scientists, enabling common approaches to distributed evaluation activities.
Seamless: Supporting assessment, evaluation, verification and understanding of physical and machine learning models across time and space scales, and from regional to global application.
Evaluation: Providing a process-oriented focus to model assessment, supporting depth of comparison between different model configurations and assessment relative to a range of observations.
Toolkit: A flexible software including code, recipes and workflow to manage a range of user requirements, underpinned by modern software development practices.

[Sylviabohnenstengel]

worked though your suggestions and included them into the documents. Still working on some changes

[Sylviabohnenstengel]

Still working on some changes so please don't merge.

[Sylviabohnenstengel]

GitHub copilot used to help with formatting

[Sylviabohnenstengel]

@Fraetor wondering if the Why CSET? section under background is becoming obsolete.

[jfrost-mo]

The "Why CSET" page is intended to provide detailed justification for CSET without overwhelming people on the documentation landing page. So I'm not sure its becoming obsolete, but it may need updating to reflect CSET's current position.

[Sylviabohnenstengel]

happy with changes

[jfrost-mo]

I think the documentation landing page (index.rst) is probably getting a little bit overwhelmed with detail. My suggestion would be to cut it down, so it has the same content as the README, and move the additional detail to the why-cset page. Then have a link from the index to the why-cset page.

This way, people who are already convinced are not overwhelmed with excessive detail or background, while those that desire it can find out more about the rational.

[jfrost-mo]

I've made some changes in #1831. If you are happy with them you should be able to merge that PR into this one.

[jfrost-mo]

As Sylvia is unavailable I've merge in my suggested changes so we can get the December release out.

Changes have been addressed.