Correct README and bump version to 0.9.1

[hexcowboy]

Summary

• correct the runtime documentation: the legacy async-std-comp feature now selects Redis's Smol/Rustls backend
• document the standalone Tokio installation accurately
• keep the primary usage example and link to the repository's example files
• remove the duplicate inline Redis Cluster sample
• clarify that cluster seed URIs describe one logical quorum backend
• fix the Redis documentation link, extend-script source lines, test commands, and example prerequisites
• bump the crate and README version references from 0.9.0 to 0.9.1

Why

The README retained runtime wording and example instructions from older Redis crate versions. In particular, it described the default backend as async-std even though the dependency now uses smol-rustls-comp, and it implied that the standalone Docker Compose file also supported the cluster example.

Impact

This is a documentation and patch-version release update. The library implementation and public API are unchanged.

Validation

• cargo hack --feature-powerset check (10 combinations passed)
• cargo test --all-features --all-targets (29 passed)
• cargo test --all-targets (25 passed)
• cargo clippy --all-features --all-targets -- -D warnings
• RUSTDOCFLAGS='-D warnings' cargo doc --no-deps --all-features
• cargo fmt --all -- --check
• cargo publish --dry-run --allow-dirty