Improve docs and examples #2950

Job	Run time
Check cargo fmt	30s
cargo check	9m 42s
build with wasm-pack	2m 18s
cargo test (macos)	11m 8s
cargo test (macos-aarch64)	6m 9s
Verify Vendored Code	41s
Verify MSRV (Min Supported Rust Version)	7m 29s
cargo test (win64)	18m 29s
cargo test datafusion-cli (amd64)	3m 35s
cargo test (amd64)	8m 26s
circular dependency check	2m 33s
cargo test doc (amd64)	11m 41s
cargo examples (amd64)	10m 50s
cargo doc	4m 5s
Run sqllogictest with Postgres runner	3m 7s
verify benchmark results (amd64)	10m 9s
check Cargo.toml formatting	2m 49s
clippy	4m 57s
check configs.md is up-to-date	2m 31s
cargo test hash collisions (amd64)	8m 48s
cargo test pyarrow (amd64)	2m 43s
	2h 12m 40s

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