Add follows to flake nix

[jaredponn]

Some numbers to back this up:

Before the PR we have:

$ time nix flake lock
real    0m10.355s
user    0m10.173s
sys 0m0.150s

$ cat flake.lock | jq '.nodes | keys' | grep nixpkgs | wc -l
374

After the PR we have:

$ cat flake.lock | jq '.nodes | keys' | grep nixpkgs | wc -l
190

$ time nix flake lock
real    0m3.045s
user    0m3.011s
sys 0m0.028s