explain performStream variants via marble diagram

[stevekrouse]

Closes #95.

I think the diagram says it all and we don't need any more words. Does this work for y'all?

[codecov[bot]]

Codecov Report

Merging #57 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #57   +/-   ##
=======================================
  Coverage   94.21%   94.21%           
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  Files          13       13           
  Lines        1228     1228           
  Branches      105      105           
=======================================
  Hits         1157     1157           
  Misses         71       71

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