[WIP] Rewriting ContentBundle docs

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | yes
| Applies to    | all
| Fixed tickets | part of #262 

 - [ ] Classes?
 - [x] Structure?
 - [ ] Examples?
 - [ ] Standards?
 - [ ] Reference Config?
 - [ ] Understandable?
 - [ ] Advanced topics?
 - [ ] Text?