[de] Improve translation, translate chapter, ...

- Fix typos in chapter 3, 3.1, 4, 4.1, 7, 7.1, 7.2, 7.3, 
- First translation of chapter 4.5 - 4.11, 7.4, 7.5
- Add respectively update english orginal text in all chapters (english text as comment). English text is no longer present in german translation. If a chapter is not translated the chapter contains no text.
- Explain workflow and current translation state in README file