[Tails-l10n] (review)[de] Documentation index

Hi,
I updated the changed headers in from the index files of the doc.

Please review:

https://gitlab.com/spriver/tails.git
branch: de_doc
HEAD commit: b247f2225e Updated changed strings

Affected files:
wiki/src/doc.de.po
wiki/src/doc/advanced_topics.index.de.po
wiki/src/doc/advanced_topics/virtualization.de.po
wiki/src/doc/first_steps.index.de.po


Cheers!
spriver