Require tests to pass before committing OR add directions to README for devs to add it optionally

[jasongitmail]

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Via stage-linted. This will require tests to pass before committing to Git:

  "lint-staged": {
    "**/*": [
      "prettier --write --ignore-unknown"
    ],
    "**/*.js": [
      "node --experimental-vm-modules ./node_modules/.bin/jest --bail --findRelatedTests"
    ]
  }

[jasongitmail]

Set it up to run tests against only staged files: npm run test:staged

[jasongitmail]

Discussed with Yoni. Closing for now because maybe too opinionated.