readme: add project layout

[travisjeffery]

No description provided.

[codecov]

Codecov Report

Merging #71 into master will increase coverage by 0.12%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #71      +/-   ##
==========================================
+ Coverage   48.81%   48.94%   +0.12%     
==========================================
  Files          18       18              
  Lines        1561     1561              
==========================================
+ Hits          762      764       +2     
+ Misses        718      716       -2     
  Partials       81       81

Impacted Files	Coverage Δ
broker/replicator.go	92.98% <0%> (+3.5%)	⬆️

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