Update README.md

[chernser]

Summary

• Removes broken nightly build badge

Checklist

Delete items not relevant to your PR:

• Closes #
• Unit and integration tests covering the common scenarios were added
• A human-readable description of the changes was provided to include in CHANGELOG
• For significant changes, documentation in https://github.com/ClickHouse/clickhouse-docs was updated with further explanations or tutorials

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Note

Low Risk
Documentation-only change with no runtime or security impact.

Overview
Removes the Nightly Build shield badge from the top of README.md that linked to Sonatype snapshots, because it was broken.

Release and download badges are unchanged; nightly install info remains in the Installation section as a plain link.

^{Reviewed by Cursor Bugbot for commit 327531a. Bugbot is set up for automated code reviews on this repo. Configure here.}

[github-actions]

Repository collaborators can run the JMH benchmark suite against this PR by commenting:

/benchmark

Optional regression threshold override (Δ% on Time or Alloc/op; defaults to 10%):

/benchmark threshold=15

Only one benchmark run per PR is active at a time — issuing a new /benchmark comment cancels the previous run. After the run finishes a separate comment will be posted comparing it against the latest scheduled run on main; the PR check fails if any benchmark regresses by more than the threshold.