improve docs

[joamatab]

fixes #2834

thank you @sebastian-goeldi

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[codecov]

Codecov Report

Attention: Patch coverage is 63.63636% with 12 lines in your changes missing coverage. Please review.

Project coverage is 68.96%. Comparing base (34ccc99) to head (400a7a1).
Report is 1 commits behind head on main.

Files	Patch %	Lines
gdsfactory/samples/12_component_refs.py	16.66%	10 Missing ⚠️
gdsfactory/component.py	0.00%	1 Missing ⚠️
gdsfactory/samples/05_remove_layers.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2836      +/-   ##
==========================================
- Coverage   68.98%   68.96%   -0.02%     
==========================================
  Files         299      298       -1     
  Lines       15345    15348       +3     
  Branches     2244     2244              
==========================================
  Hits        10585    10585              
- Misses       4158     4161       +3     
  Partials      602      602              

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