docs: Polish docs for Operator, Reader and Writer #2299

Job	Run time
check_clippy	3m 41s
check_docs	3m 20s
build_all_features	4m 52s
build_default_features (ubuntu-latest)	42s
check_msrv	33s
build_default_features (macos-latest)	36s
build_default_features (windows-latest)	1m 16s
build_all_platforms (ubuntu-latest)	2m 32s
build_under_wasm	46s
build_all_platforms (macos-latest)	2m 27s
unit	6m 48s
build_all_platforms (windows-latest)	4m 49s
	32m 22s

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