added comments to flake.nix

flake.nix

@@ -18,6 +18,7 @@
     forEachSystem = nixpkgs.lib.genAttrs systems;
     forEachPkgs = lambda: forEachSystem (system: lambda (pkgsFor system));
   in {
+    # development tooling
     devShells = forEachPkgs (pkgs: {
       default = pkgs.mkShell {
         packages = with pkgs; [
@@ -31,6 +32,7 @@
       };
     });
 
+    # library contents
     nixosModules.default = self.nixosModules.syncthing;
     nixosModules.syncthing = import ./lib/nixos-module.nix;
 
@@ -49,6 +51,7 @@
         );
     };
 
+    # example configuration
     nixosConfigurations = {
       default = nixpkgs.lib.nixosSystem {
         specialArgs = {inherit self;};