docs: expand on what `Requests` contains (#1564) #4777

Job	Run time
check no_std	53s
docs	1m 56s
cfg-check	1m 13s
clippy	1m 23s
doctest	2m 45s
feature-checks	8m 11s
fmt	13s
test ubuntu-latest stable --no-default-features	2m 23s
test ubuntu-latest stable	2m 19s
wasm-unknown	2m 9s
wasm-wasi	3m 6s
test ubuntu-latest stable --all-features	3m 3s
test ubuntu-latest nightly --no-default-features	2m 40s
test ubuntu-latest nightly	2m 28s
test ubuntu-latest nightly --all-features	2m 58s
test ubuntu-latest 1.79 --no-default-features	1m 26s
test ubuntu-latest 1.79	1m 36s
test windows-latest stable --no-default-features	5m 51s
test windows-latest stable	6m 37s
test windows-latest stable --all-features	6m 42s
test windows-latest nightly --no-default-features	6m 36s
test windows-latest nightly	6m 8s
test windows-latest nightly --all-features	7m 7s
test windows-latest 1.79 --no-default-features	3m 21s
test windows-latest 1.79	3m 7s
	1h 26m 11s

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