Documentation of detailed behaviors

[koide3]

Add documentation of detailed behaviors including some corner cases.

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

Attention: Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 93.16%. Comparing base (76b2f00) to head (57e841d).
Report is 1 commits behind head on master.

Files	Patch %	Lines
include/small_gicp/util/downsampling.hpp	50.00%	1 Missing ⚠️
include/small_gicp/util/downsampling_tbb.hpp	75.00%	1 Missing ⚠️

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #82      +/-   ##
==========================================
- Coverage   93.34%   93.16%   -0.19%     
==========================================
  Files          38       38              
  Lines         857      863       +6     
  Branches       77       78       +1     
==========================================
+ Hits          800      804       +4     
- Misses         57       59       +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.