Address remaining comments on the book from Jakob and Nicolai

Description:

Remaining issues regarding editing the book overall (remaining from #58 #56 )

[ ] Chapter 1 page: State explicitly that these are learning objectives. And use consistent format for learning objective for all chapters.
[ ] Then other chapters have empty startpages eg chapter 2 would benefit from also having a short intro and chapter learning objectives added: https://amal-ghamdi.github.io/CUQI-Book-test/chapter02/chapter02.html
[ ] Consider splitting long pages into multiple shorter (e.g. separate install out from the long overview page). Two reasons for this. One: Long pages can be overwhelming. Two: Makes it easier to find, since each shorter page will appear in the menu on the left. Another example is Five little stories. They make a nice package, but page is very long. Better split into five pages?
[ ] The five little stories are really great as it nicely conveys insights about different samplers. I wonder if it would be beneficial to organize as five separate, shorter files, to keep more manageable and allow navigating them in menu?
[ ] Some titles long, look confusing eg chap 3 Sampling with CUQIpy: Two target … Short concise titles will make menu make clearly structured. (addressed partially #47)
[ ] Consider using Subtitle numbers e.g 3.1, 3.2 for parts of chapters/pages, to help organize and make it easy to refer to specific material by section number rather than only by a string heading.
[ ] I hadn't noticed the colours used for section and subsection headings and didn't realise colour had significance. Can see it is useful in the menu on the right for overview. Suggest to make the colours more distinct.
[ ] remove subheaders (e.g. 1.1., 1.2.) from the notebook content section at the beginning of the notebook and keep only the main headers (e.g. 1., 2., 3.) (partially addressed)
[ ] Perhaps this is personal preferance, but I was thinking perhaps the convolution forward model should be explained first rather than the heat equation.

DoD:

[ ] The issues above are addressed
[ ] The updates are reviewed and merged

CUQI-DTU / CUQI-Book

Address remaining comments on the book from Jakob and Nicolai #73

Description:

DoD: