Improve documentation of Lwt_stream #723

Job	Run time
build (ubuntu-latest, 4.08.x, true, true, *.opam )	7m 26s
build (ubuntu-latest, 4.08.x, false, true, *.opam )	6m 37s
build (ubuntu-latest, 4.09.x, true, true, *.opam )	7m 45s
build (ubuntu-latest, 4.09.x, false, true, *.opam )	7m 38s
build (ubuntu-latest, 4.10.x, true, true, *.opam )	9m 17s
build (ubuntu-latest, 4.10.x, false, true, *.opam )	6m 43s
build (ubuntu-latest, 4.11.x, true, true, *.opam )	8m 9s
build (ubuntu-latest, 4.11.x, false, true, *.opam )	9m 57s
build (ubuntu-latest, 4.12.x, true, true, *.opam )	7m 48s
build (ubuntu-latest, 4.12.x, false, true, *.opam )	6m 37s
build (ubuntu-latest, 4.13.x, true, true, *.opam )	4m 44s
build (ubuntu-latest, 4.13.x, false, true, *.opam )	6m 53s
build (ubuntu-latest, 4.14.x, true, true, *.opam )	4m 56s
build (ubuntu-latest, 4.14.x, false, true, *.opam )	4m 10s
build (ubuntu-latest, 5.0.x, true, true, *.opam )	6m 23s
build (ubuntu-latest, 5.0.x, false, true, *.opam )	4m 0s
build (ubuntu-latest, ocaml-variants.4.14.0+options,ocaml-option-flambda,ocaml-option-musl,ocaml-...	5m 50s
build (macos-latest, 4.14.x, true, true, *.opam )	14m 16s
build (windows-latest, 4.14.x, false, true, *.opam )	6m 29s
build (ubuntu-latest, 4.08.x, true, false, *.opam !lwt_ppx.opam )	7m 13s
build (macos-latest, 4.08.x, true, false, *.opam !lwt_ppx.opam )	15m 18s
build (windows-latest, 4.08.x, false, false, *.opam !lwt_ppx.opam )	4m 18s
	2h 42m 27s

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