Add instructions for updating licenses

[jihoonson]

Description

Managing licenses is hard.. This PR adds an instruction for how to update licenses.

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This PR has:

• been self-reviewed.
  • using the concurrency checklist (Remove this item if the PR doesn't have any relation to concurrency.)
• added documentation for new or modified features or behaviors.
• added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
• added or updated version, license, or notice information in licenses.yaml
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.
• added integration tests.
• been tested in a test Druid cluster.

[capistrant]

This is awesome content and very informative! I don't know if I'm qualified to review since it is all new information to me. All of the content made sense to me, an uninformed dev, so that's good 👍

[clintropolis]

lgtm, thanks for adding 👍