fix: update help text for model configuration argument

[gagb]

This pull request includes a small change to the python/packages/magentic-one-cli/src/magentic_one_cli/_m1.py file. The change modifies the help message for the --config argument to remove the part about leaving it empty to print a sample configuration. This is already handled by --sample-config.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.74%. Comparing base (0355b22) to head (0c774e9).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5533   +/-   ##
=======================================
  Coverage   78.74%   78.74%           
=======================================
  Files         167      167           
  Lines       10004    10004           
=======================================
  Hits         7878     7878           
  Misses       2126     2126           

Flag	Coverage Δ
unittests	78.74% <ø> (ø)

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