bevy_ecs: Add doc example for par_iter_mut (#11311) #35462

Job	Run time
build (windows-latest)	3m 55s
check-bevy-internal-imports	4s
build (ubuntu-latest)	2m 21s
check-doc	4m 53s
build (macos-latest)	3m 0s
check-missing-examples-in-docs	38s
ci	1m 45s
miri	6m 34s
run-examples-on-windows-dx12	11m 47s
toml	5s
check-missing-features-in-docs	36s
markdownlint	1m 18s
check-compiles	2m 18s
msrv	1m 0s
build-wasm	36s
	40m 50s

Provide feedback