nixd/docs/editor-setup: fix lspconfig link #3211

Job	Run time
nix-build-develop-clang (none, release, true)	3m 4s
nix-build-develop-gcc (none, release, true)	3m 4s
nix-build-develop-clang (none, release, false)	3m 6s
nix-build-develop-gcc (none, release, false)	3m 9s
nix-build-develop-clang (none, debug, true)	2m 47s
nix-build-develop-gcc (none, debug, true)	2m 56s
nix-build-develop-clang (none, debug, false)	2m 51s
nix-build-develop-gcc (none, debug, false)	3m 0s
nix-build-develop-gcc (address, release, true)	4m 44s
nix-build-develop-gcc (address, release, false)	4m 45s
nix-build-develop-gcc (address, debug, true)	3m 59s
nix-build-develop-gcc (address, debug, false)	4m 2s
nix-build-develop-gcc (undefined, release, true)	4m 8s
nix-build-develop-gcc (undefined, release, false)	4m 9s
nix-build-develop-gcc (undefined, debug, true)	3m 17s
nix-build-develop-gcc (undefined, debug, false)	3m 22s
	56m 23s

Provide feedback