Improve description of function migration (#12743) #22

Job	Run time
Check cargo fmt	42s
cargo check	10m 32s
build with wasm-pack	2m 45s
cargo test (macos)	10m 56s
cargo test (macos-aarch64)	10m 26s
Verify MSRV (Min Supported Rust Version)	8m 42s
Verify Vendored Code	40s
cargo test (win64)	58m 9s
cargo test datafusion-cli (amd64)	4m 13s
cargo test (amd64)	10m 47s
cargo examples (amd64)	13m 47s
check Cargo.toml formatting	3m 3s
clippy	4m 2s
check configs.md and ***_functions.md is up-to-date	3m 7s
cargo test hash collisions (amd64)	17m 34s
cargo doc	4m 20s
cargo test doc (amd64)	15m 21s
Run sqllogictest with Postgres runner	3m 43s
cargo test pyarrow (amd64)	3m 0s
verify benchmark results (amd64)	12m 42s
	3h 18m 31s

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