[example] Adds document about how to trace gpt2 model

[frankfliu]

Description

Brief description of what this PR is about

• If this change is a backward incompatible change, why must this change be made?
• Interesting edge cases to note here

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.22%. Comparing base (0fa0db2) to head (d313389).

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Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3028      +/-   ##
============================================
- Coverage     72.30%   72.22%   -0.09%     
+ Complexity     7294     7290       -4     
============================================
  Files           722      722              
  Lines         32508    32508              
  Branches       3395     3395              
============================================
- Hits          23506    23479      -27     
- Misses         7382     7411      +29     
+ Partials       1620     1618       -2     

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