docs: add note about write permissions for auth scripts on the filesystem

[lexops]

This PR adds a note to the documentation addressing the issue where authentication scripts may require write access to the filesystem, which can lead to errors like [Errno 30] Read-only file system.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.53%. Comparing base (720f495) to head (576c850).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #880   +/-   ##
=======================================
  Coverage   75.53%   75.53%           
=======================================
  Files          31       31           
  Lines        3151     3151           
=======================================
  Hits         2380     2380           
  Misses        636      636           
  Partials      135      135           

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[chengfang]

related discussion:
#720
#112