minor: Add link to example for `AsyncSchemaProvider` #36749

Job	Run time
build with wasm-pack	3m 28s
cargo test (macos-aarch64)	12m 39s
Check License Header	2m 21s
linux build test	4m 2s
Check cargo fmt	46s
Verify MSRV (Min Supported Rust Version)	9m 9s
Verify Vendored Code	50s
cargo check no default features	8m 22s
cargo check datafusion	4m 53s
cargo check functions	1m 35s
cargo doc	4m 40s
cargo test (amd64)	12m 33s
cargo test datafusion-cli (amd64)	5m 16s
cargo test doc (amd64)	18m 38s
Run sqllogictest with Postgres runner	4m 55s
verify benchmark results (amd64)	8m 24s
cargo examples (amd64)	15m 27s
check Cargo.toml formatting	3m 11s
clippy	6m 52s
check configs.md and ***_functions.md is up-to-date	4m 7s
cargo test pyarrow (amd64)	3m 47s
	2h 15m 55s

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