docs(cookie): how to get frontend cookie

[dead-horse]

Checklist

• npm test passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

Description of change

[codecov]

Codecov Report

Merging #2542 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2542   +/-   ##
=======================================
  Coverage   99.63%   99.63%           
=======================================
  Files          29       29           
  Lines         815      815           
=======================================
  Hits          812      812           
  Misses          3        3

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