update documentation, add example on how to add multiple news feeds with different configurations (different content per feed).

- Group by Tags: Not respecting the rootline, if the option onlyNewsWithinThisPageSection is true.
- Group by Categories: Not resprecting the rootline, if the option onlyNewsWithinThisPageSection is true. Also not respecting the multi language behaviour of the TYPO3 9 pages table.
- No grouping:  Not respecting the rootline, if the option onlyNewsWithinThisPageSection is true.

This is because in TYPO3 9, the page translations are themselves real page
records and would get mixed up then sorting via uid. The more safe way to
sort those is to use the sorting, thich also represents the sorting in the
backend page tree.

[BUGFIX] Fix the selection of news by category if categories are translated but news are just set to "force" by languagevisibility