Fix links in German README

There were three links that weren't displayed correctly due to incorrect
references:
 - the Windows release link to `README.md#windows`
 - 2 links that expected a German reference but got an English reference

PR #3026 <https://github.com/Genymobile/scrcpy/pull/3026>

Signed-off-by: Romain Vimont <rom@rom1v.com>