Fix: Some spelling corrections

[rgxdev]

This pull request makes several minor language and phrasing improvements to the German README, focusing on consistency and readability. The main changes standardize the use of "am besten" instead of "am Besten," ensure consistent lowercase usage after colons, and correct some capitalization and phrasing for clarity.

Language and phrasing improvements:

• Standardized "am besten" (lowercase) throughout the README for consistency and proper German usage. [1] [2] [3] [4] [5]
• Updated section headers and sentences to use lowercase after colons, e.g., "In der folgenden Challenge..." instead of "In der Folgenden Challenge..." and "Achtung süße Katzenbilder!" instead of "Achtung Süße Katzenbilder!" [1] [2]
• Fixed minor typographical errors, such as removing duplicate words ("und und warte" → "und warte").
• Improved phrasing for clarity, such as "Offiziell ist am besten" instead of "Offiziell ist am Besten."