chore(example): Clarify that 'packages' can override #1059

Job	Run time
configure	1s
nix (aarch64-linux, dev)	13s
nix (aarch64-linux, doc)	42s
nix (aarch64-linux, example)	28s
nix (aarch64-linux, haskell-parsers-test)	7s
nix (aarch64-linux, test-otherOverlays)	31s
nix (aarch64-linux, test-project-module)	28s
nix (aarch64-linux, test-settings-defaults)	27s
nix (aarch64-linux, test-simple)	16s
nix (aarch64-linux, test-with-subdir)	26s
nix (aarch64-darwin, dev)	20s
nix (aarch64-darwin, doc)	1m 10s
nix (aarch64-darwin, example)	1m 31s
nix (aarch64-darwin, haskell-parsers-test)	18s
nix (aarch64-darwin, test-otherOverlays)	59s
nix (aarch64-darwin, test-project-module)	1m 6s
nix (aarch64-darwin, test-settings-defaults)	1m 40s
nix (aarch64-darwin, test-simple)	1m 17s
nix (aarch64-darwin, test-with-subdir)	38s
	12m 38s

Provide feedback