Add help messages to SourceAgent

[ahuang11]

Closes #1030

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.

Project coverage is 57.68%. Comparing base (60ea02f) to head (fbec13d).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
lumen/ai/agents.py	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1037      +/-   ##
==========================================
- Coverage   57.70%   57.68%   -0.03%     
==========================================
  Files         109      109              
  Lines       14197    14202       +5     
==========================================
  Hits         8192     8192              
- Misses       6005     6010       +5     

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[philippjfr]

Thanks, good suggestion!