added readme for supabase migrations

[abyan-n]

Description

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Adds readme for supabase migrations

How Has This Been Tested?

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Please describe the tests that you ran to verify your changes. If they are unit
tests, provide the file name the tests are in. If they are not unit tests,
describe how you tested the change.
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Checklist

• [X ] I have performed a self-review of my code
• [X ] I have reached out to another developer to review my code
• [X ] I have commented my code, particularly in hard-to-understand areas
• [X ] New and existing unit tests pass locally with my changes

[benjaspet]

Great work!