Add 'test' section to README.md

[rahul2393]

Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:

• Make sure to open an issue as a bug/issue before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea
• Ensure the tests and linter pass
• Code coverage does not decrease (if any source code was changed)
• Appropriate docs were updated (if necessary)
• Rollback plan is reviewed and LGTMed
• All new data plane features have a completed end to end testing plan

Fixes #<issue_number_goes_here> ☕️

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