docs: added more info to the buildcmake page. Merged cmake.md with #820.

[Jaskowicz1]

This PR adds more information to the cmake.md page (buildcmake) whilst also improving the wording. This PR also merges the changes from #820 related to cmake.md.

Documentation change checklist

• My documentation changes follow the same style as the rest of the documentation and any examples follow the coding style guide.
• I tested that my change works before raising the PR (via running oxygen, and testing examples).
• I have not moved any existing pages or changed any existing URLs without strong justification as to why.
• I have not generated content using AI or a desktop utility such as grammarly.

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