add nix substituters and update nix.conf

pr-28.patch

@@ -1,5 +1,5 @@
 diff --git a/base.nix b/base.nix
-index 7eaee32..8e317ec 100644
+index 7eaee32..3a2a0a9 100644
 --- a/base.nix
 +++ b/base.nix
 @@ -27,6 +27,11 @@ with lib;
@@ -14,8 +14,23 @@ index 7eaee32..8e317ec 100644
      not-os.simpleStaticIp = mkOption {
        type = types.bool;
        default = false;
-@@ -93,8 +98,14 @@ with lib;
-         build-cores = 4
+@@ -86,15 +91,25 @@ with lib;
+       "nix/nix.conf".source = pkgs.runCommand "nix.conf" {} ''
+         extraPaths=$(for i in $(cat ${pkgs.writeReferencesToFile pkgs.runtimeShell}); do if test -d $i; then echo $i; fi; done)
+         cat > $out << EOF
+-        build-use-sandbox = true
++        auto-optimise-store = true
+         build-users-group = nixbld
+-        build-sandbox-paths = /bin/sh=${pkgs.runtimeShell} $(echo $extraPaths)
+-        build-max-jobs = 1
+-        build-cores = 4
++        cores = 0
++        extra-sandbox-paths = /bin/sh=${pkgs.runtimeShell} $(echo $extraPaths)
++        max-jobs = auto
++        sandbox = true
++        substituters = https://cache.armv7l.xyz
++        trusted-public-keys = cache.armv7l.xyz-1:kBY/eGnBAYiqYfg0fy0inWhshUo+pGFM3Pj7kIkmlBk=
++        trusted-users = root
          EOF
        '';
 +      "ssl/certs/ca-certificates.crt".source = "${pkgs.cacert}/etc/ssl/certs/ca-bundle.crt";