index.rst.de: Revise German homepage

- Replace some wordings with more idiomatic/fluent German while trying
  to stay close to the original English wording
- Standardize indentation
- Replace "false friends"
- Fix one capitalization and an untranslated word
Fix accidental typo
Merge pull request #34 from nsemrau/master

index.rst.de: Revise German homepage