docs: add docs for as.hclust.igraphHRG()

[maelle]

Fix #732

[codecov]

Codecov Report

Merging #733 (ae67351) into main (9fb18e1) will decrease coverage by 0.01%.
The diff coverage is n/a.

❗ Current head ae67351 differs from pull request most recent head c6ca769. Consider uploading reports for the commit c6ca769 to get more accurate results

@@            Coverage Diff             @@
##             main     #733      +/-   ##
==========================================
- Coverage   53.94%   53.93%   -0.01%     
==========================================
  Files         357      357              
  Lines       73336    73281      -55     
==========================================
- Hits        39559    39523      -36     
+ Misses      33777    33758      -19     

Impacted Files	Coverage Δ
R/aaa-auto.R	76.44% <ø> (ø)
R/hrg.R	34.10% <ø> (ø)
src/rinterface.c	87.94% <ø> (+12.05%)	⬆️
src/rinterface_extra.c	68.82% <ø> (-18.59%)	⬇️

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