[docs] add output.PreserveModulesRoot to big list of options

[davidroeca]

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:

Description

Adds docs that were missed in #3786

[codecov]

Codecov Report

Merging #3792 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3792   +/-   ##
=======================================
  Coverage   97.03%   97.03%           
=======================================
  Files         185      185           
  Lines        6478     6478           
  Branches     1877     1877           
=======================================
  Hits         6286     6286           
  Misses        101      101           
  Partials       91       91           

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[lukastaegert]

Looks good, thanks a lot!