[REVIEW] Update LogisticRegression documentation

[viclafargue]

Closes #3671

[dantegd]

@gpucibot merge

[codecov-io]

Codecov Report

Merging #3677 (287c597) into branch-0.19 (8316807) will increase coverage by 8.19%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           branch-0.19    #3677      +/-   ##
===============================================
+ Coverage        74.11%   82.31%   +8.19%     
===============================================
  Files              214      227      +13     
  Lines            16660    17541     +881     
===============================================
+ Hits             12348    14439    +2091     
+ Misses            4312     3102    -1210     

Flag	Coverage Δ
dask	46.40% <ø> (?)
non-dask	74.28% <ø> (+0.16%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
python/cuml/linear_model/logistic_regression.pyx	89.16% <ø> (ø)
python/cuml/common/numba_utils.py	0.00% <0.00%> (ø)
python/cuml/internals/global_settings.py	100.00% <0.00%> (ø)
python/cuml/cluster/kmeans_mg.pyx	82.60% <0.00%> (ø)
python/cuml/linear_model/base_mg.pyx	100.00% <0.00%> (ø)
python/cuml/decomposition/pca_mg.pyx	96.36% <0.00%> (ø)
python/cuml/cluster/dbscan_mg.pyx	100.00% <0.00%> (ø)
python/cuml/decomposition/tsvd_mg.pyx	100.00% <0.00%> (ø)
python/cuml/neighbors/kneighbors_classifier_mg.pyx	100.00% <0.00%> (ø)
python/cuml/common/opg_data_utils_mg.pyx	98.97% <0.00%> (ø)
... and 71 more

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[dantegd]

rerun tests