Fix by doc the behavior of the GitHub authenticator.

[stefanoborini]

Fixes #368

[codecov-io]

Codecov Report

Merging #386 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #386   +/-   ##
======================================
  Coverage    95.3%   95.3%           
======================================
  Files          92      92           
  Lines        3941    3941           
  Branches      255     255           
======================================
  Hits         3756    3756           
  Misses        128     128           
  Partials       57      57

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