Fix #2961: add basic docstring to clifford_optimized_circuit()

[mhucka]

This adds a basic documentation string to the function clifford_optimized_circuit() in the file cirq-core/cirq/contrib/paulistring/clifford_optimize.py.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.37%. Comparing base (7a0a7be) to head (9c09585).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7663      +/-   ##
==========================================
- Coverage   99.37%   99.37%   -0.01%     
==========================================
  Files        1082     1082              
  Lines       96708    96708              
==========================================
- Hits        96102    96101       -1     
- Misses        606      607       +1     

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[pavoljuhas]

LGTM with fixed inline comment.