Meson

docs: add nixd worker model #1767

Job	Run time
nix-build-develop-clang (none, release, true)	2m 54s
nix-build-develop-gcc (none, release, true)	3m 8s
nix-build-develop-clang (none, release, false)	2m 53s
nix-build-develop-gcc (none, release, false)	3m 14s
nix-build-develop-clang (none, debug, true)	2m 45s
nix-build-develop-gcc (none, debug, true)	3m 2s
nix-build-develop-clang (none, debug, false)	2m 41s
nix-build-develop-gcc (none, debug, false)	2m 58s
nix-build-develop-gcc (undefined, release, true)	6m 31s
nix-build-develop-gcc (undefined, release, false)	6m 34s
nix-build-develop-gcc (undefined, debug, true)	3m 33s
nix-build-develop-gcc (undefined, debug, false)	3m 45s
	43m 58s

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