docs(example): add ultrafast enzyme example

[Nimrais]

Showcase how to obtain a fast inference with Enzyme.jl.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.38%. Comparing base (c0b2794) to head (c1cc817).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #75   +/-   ##
=======================================
  Coverage   99.38%   99.38%           
=======================================
  Files          12       12           
  Lines         486      486           
=======================================
  Hits          483      483           
  Misses          3        3           

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