Add three nodes example

[arcusfelis]

As asked in https://erlangforums.com/t/cets-clustered-ets-replication/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.92%. Comparing base (bc61bd9) to head (86f9ff3).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #56      +/-   ##
==========================================
+ Coverage   98.80%   98.92%   +0.11%     
==========================================
  Files          11       11              
  Lines         834      834              
==========================================
+ Hits          824      825       +1     
+ Misses         10        9       -1     

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