doc: add link on logo to README
Checklist
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documentation is changed or added -
commit message follows commit guidelines
This is to override GitHub's default behaviour that links to the image's source file, which isn't very helpful in our case.
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
This is to override GitHub's default behaviour that links to the image's source file, which isn't very helpful in our case.