docs: improve docs content

[tromika]

What kind of change does this pull request introduce?

Improving the docs, fixing typos, and making sure the documentation is clear.

What is the new behavior?

The docs are crystal clear.

Checklist

• Documentation
• Ready to be merged
  

[tromika]

@sannek added some improvements from my side. For the rest, for me, it's logically clear. On the other hand, I can't assess in many cases it's clear enough to use it.

[sannek]

Looks good to me! I suppose I should also use this branch to do my copy editing/nitpicking, because otherwise i'm looking at dated stuff?

I'll fix the merge conflict and go over it as well.

[tromika]

Yes please! Also I'm still planning to go through on this once again. So it's a good collaborative experience in CSB projects! Thanks!

[sannek]

Actually - i realised that my interactive examples aren't on this branch - so we really should merge this one asap and get on a new branch.

I'm still finishing up on the custom-content guide, but I'm a bit stuck on it so figured I'd take a little break to edit the rest first.