Minor: Improve `DataFrame` docs, add examples #23083

Job	Run time
cargo check	6m 39s
Check cargo fmt	57s
build with wasm-pack	2m 34s
cargo test (macos)	23m 38s
Verify MSRV (Min Supported Rust Version)	8m 20s
Verify Vendored Code	1m 6s
cargo test (win64)	42m 40s
cargo test doc (amd64)	10m 44s
check configs.md is up-to-date	2m 41s
clippy	5m 10s
check Cargo.toml formatting	1m 50s
cargo test hash collisions (amd64)	9m 48s
cargo doc	4m 18s
cargo test (amd64)	9m 41s
cargo test datafusion-cli (amd64)	4m 12s
cargo examples (amd64)	8m 51s
Run sqllogictest with Postgres runner	3m 36s
cargo test pyarrow (amd64)	2m 34s
verify benchmark results (amd64)	10m 32s
	2h 39m 51s

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