Clarify license of buf.build assets

[luisgerhorst]

🐛 Bug Report

Would it be possible to add a license as recommended by https://buf.build/docs/bsr/module/manage/#module-documentation ? I guess the default would be that the assets are under the same license as the project, however, common license checkers do not appear to detect this properly when a Go module uses the buf.build asset as a dependency.

To Reproduce

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Expected behavior

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Actual Behavior

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Your Environment

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