add example with multiple bundles

[maxbeatty]

adds example with multiple bundles (main and cli) using separate calls to ncc build. module is admittedly simple to keep focus on build process in package.json

ref #50

[codecov-io]

Codecov Report

Merging #201 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #201   +/-   ##
=======================================
  Coverage   67.87%   67.87%           
=======================================
  Files          12       12           
  Lines         579      579           
=======================================
  Hits          393      393           
  Misses        186      186

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[rauchg]

Epic! Thanks so much @maxbeatty