docs: add a link to the Electron docs for darwinDarkModeSupport

[malept]

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Summarize your changes:

Fixes #1107.

[codecov-io]

Codecov Report

Merging #1110 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #1110   +/-   ##
======================================
  Coverage     100%    100%           
======================================
  Files          14      14           
  Lines         712     712           
======================================
  Hits          712     712

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