release-23.1: README: Update licensing information

[rail]

Backport 1/1 commits from #158903 on behalf of @rail.

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Fixes: CRDB-45643
Release note: none

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Release justification: readme update

[blathers-crl]

Thanks for opening a backport.

Before merging, please confirm that it falls into one of the following categories (select one):

• Non-production code changes. Includes test-only changes, build system changes, etc.
• Fixes for serious issues. Defined in the policy as correctness, stability, or security issues, data corruption/loss, significant performance regressions, breaking working and widely used functionality, or an inability to detect and debug production issues.
• Other approved changes. These changes must be gated behind a disabled-by-default feature flag unless there is a strong justification not to.

Add a brief release justification to the PR description explaining your selection.

Also, confirm that the change does not break backward compatibility and complies with all aspects of the backport policy.

All backports must be reviewed by the TL and EM for the owning area.

[blathers-crl]

❌ PR #158926 does not comply with backport policy

Confidence: high
Explanation: The pull request involves a change to README.md, which is not a non-production file under the specified non-production file patterns. Furthermore, the PR does not meet the critical bug criteria as outlined in the CockroachDB Backport Policy. The change is described as a 'readme update' and thus does not relate to any stability, security issues, data corruption/loss, significant performance regressions, incorrect database results, or improvements in debugging capabilities. Additionally, there are no indications of this change being gated behind a feature flag or involving new cluster settings which are disabled by default. Therefore, as this change does not qualify under the critical bug fix or feature flag requirements, it is non-compliant. Also, the release justification provided ('readme update') does not justify a bypass of the backport criteria. Lastly, there is no evidence suggesting that this change would cause backward compatibility issues.
Recommendation: Reconsider the backport or provide a more substantial justification for backporting this change.

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is