Add documentation on f1, recall and precision score with averaging me...

[ahn1340]

…chanisms in api.rst. Fixes #422 .

[codecov-io]

Codecov Report

Merging #477 into development will increase coverage by 0.03%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           development     #477      +/-   ##
===============================================
+ Coverage        78.59%   78.63%   +0.03%     
===============================================
  Files              130      130              
  Lines            10088    10088              
===============================================
+ Hits              7929     7933       +4     
+ Misses            2159     2155       -4

Impacted Files	Coverage Δ
...mponents/feature_preprocessing/nystroem_sampler.py	91.17% <0%> (+5.88%)	⬆️

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