Improve documentation

Citrus already comes with a detailed and explanatory documentation, giving insights into the framework and also into the integrated communication technology. We will review the documentation’s structure and content to make it easier to navigate and focus on the features of the framework.

- [ ] #462
- [ ] #532
- [ ] #533

Start by reviewing the documentation structure and content, then read the linked issues #462, #532, and #533 to identify the intended scope. Done means the framework documentation is easier to navigate and focuses clearly on framework features, but this issue does not name specific files or tests.

Written by the indexing model from the issue text.