Allow calling @help for macros.

[piechologist]

Closes issue #37 .

I've changed the docstring and usage.md accordingly.

Thank you for writing and maintaining this package! It's an essential part of my workflow.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 20.04%. Comparing base (9e61638) to head (cabb0d8).
Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #39      +/-   ##
==========================================
- Coverage   24.67%   20.04%   -4.63%     
==========================================
  Files          15       14       -1     
  Lines         912      888      -24     
==========================================
- Hits          225      178      -47     
- Misses        687      710      +23     

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[ronisbr]

Thanks!