docs: mention `testcontainers-modules` #644

Job	Run time
msrv (build --all-features)	2m 30s
test (test --all-features)	3m 27s
msrv (build --no-default-features)	3m 22s
lint	2m 26s
test (test --no-default-features)	3m 21s
style	10s
	15m 16s

Provide feedback