Fix documentation issues where RRi is mentioned instead of rpeaks.

[lamourj]

Doc was inconsistent with the code, where the doc mentions that the RRi is expected while the code expects the rpeaks, which get transformed to RRi afterwards.

Other pull request to come that allow to input either RRi or Rpeaks.

[codecov[bot]]

Codecov Report

Merging #51 into master will increase coverage by 16.07%. The diff coverage is n/a.

@@             Coverage Diff             @@
##           master      #51       +/-   ##
===========================================
+ Coverage   37.21%   53.29%   +16.07%     
===========================================
  Files          32       32               
  Lines        3079     1910     -1169     
===========================================
- Hits         1146     1018      -128     
+ Misses       1933      892     -1041

Impacted Files	Coverage Δ
neurokit/bio/bio_ecg.py	66.56% <ø> (ø)	:arrow_up:
neurokit/signal/events.py	9.09% <0%> (-5.5%)	:arrow_down:
neurokit/signal/epochs.py	9.67% <0%> (-0.81%)	:arrow_down:

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[DominiqueMakowski]

Awesome! Thanks 😄