docs: invoke bash directly in test readme bash commands

[baileympearson]

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Double check the following

• Lint is passing (npm run check:lint)
• Self-review completed using the steps outlined here
• PR title follows the correct format: type(NODE-xxxx)[!]: description
  • Example: feat(NODE-1234)!: rewriting everything in coffeescript
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[PavelSafronov]

It might be nice to explicitly mention that we are running everything through bash, so even if we forget to update all references, the general guidance is still clear.