Update README sync script & Contributing instructions

[cbortz]

Context

When first contributing here, I ran into an issue here the README was out of sync after creating a new command. While this is mentioned in the instructions, the command given didn't produce a new output for me. Thus, the build failed.

After looking at the failing build in TravisCI, I found that there's an internal script with just that purpose: Updating the CLI usage in the readme file. It seemed clear to me that the README should be updated to reference the aforementioned script.

Changes

• Sets a default value in README sync script
  • Default to "README.md"
  • Update .travis.yml to reflect this change
• Update instructions for syncing README when adding a command
  • Previously set to copy the output from an aptible help call
  • Instead, leverage the README usage sync script
• Updates Contributors in README

[codecov-io]

Codecov Report

Merging #235 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #235   +/-   ##
=======================================
  Coverage   93.87%   93.87%           
=======================================
  Files          49       49           
  Lines        2009     2009           
=======================================
  Hits         1886     1886           
  Misses        123      123

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[krallin]

Thanks!