Improve doc for BodyWithConfig #2694

Job	Run time
build_versions (stable)	21s
Test	59s
Test	53s
build_versions (beta)	17s
Test (charset)	1m 10s
Test (charset)	51s
Test (cookies)	1m 11s
build_versions (1.71.1)	18s
Test (cookies)	57s
Test (socks-proxy)	58s
Test (socks-proxy)	57s
Test (gzip)	1m 1s
Test (brotli)	1m 5s
cargo-deny (aarch64-apple-ios)	19s
Test (json)	1m 10s
Test (native-tls)	1m 10s
Test (gzip)	1m 0s
Test (brotli)	1m 14s
cargo-deny (aarch64-linux-android)	18s
Test (json)	1m 2s
Docs	1m 48s
cargo-deny (i686-pc-windows-gnu)	19s
Test (native-tls)	1m 14s
cargo-deny (i686-pc-windows-msvc)	21s
Test (rustls-no-provider)	1m 12s
cargo-deny (i686-unknown-linux-gnu)	18s
Lint	41s
cargo-deny (wasm32-unknown-unknown)	19s
cargo-deny (x86_64-apple-darwin)	22s
cargo-deny (x86_64-apple-ios)	20s
cargo-deny (x86_64-pc-windows-gnu)	20s
cargo-deny (x86_64-pc-windows-msvc)	19s
cargo-deny (x86_64-unknown-linux-gnu)	24s
cargo-deny (x86_64-unknown-redox)	20s
	25m 28s

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