Minior: Add example comment on window expr #7

Job	Run time
Check cargo fmt	44s
build with wasm-pack	2m 14s
cargo check	4m 3s
cargo test (macos)	19m 5s
cargo test (macos-aarch64)	9m 57s
Verify MSRV (Min Supported Rust Version)	7m 5s
Verify Vendored Code	51s
cargo test (win64)	45m 10s
check configs.md is up-to-date	2m 33s
check Cargo.toml formatting	1m 24s
clippy	5m 29s
cargo test hash collisions (amd64)	9m 36s
cargo doc	3m 57s
cargo test (amd64)	9m 29s
cargo test datafusion-cli (amd64)	3m 39s
cargo test doc (amd64)	6m 21s
cargo examples (amd64)	8m 54s
Run sqllogictest with Postgres runner	3m 4s
cargo test pyarrow (amd64)	2m 35s
verify benchmark results (amd64)	10m 22s
	2h 36m 32s

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