docs: add elapsed middleware to an example

[caarlos0]

refs #206

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (54e6a3d) 76.40% compared to head (e3720ce) 76.40%.

❗ Current head e3720ce differs from pull request most recent head c7c2d88. Consider uploading reports for the commit c7c2d88 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #212   +/-   ##
=======================================
  Coverage   76.40%   76.40%           
=======================================
  Files          17       17           
  Lines         907      907           
=======================================
  Hits          693      693           
  Misses        160      160           
  Partials       54       54           

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