Add comments to flake.nix

flake.nix

@@ -1,9 +1,18 @@
+# This is a system configuration template that uses nix-bitcoin.
+#
+# You can adapt this to an existing system flake by copying the parts
+# relevant to nix-bitcoin.
+#
+# Make sure to check and edit all lines marked by 'FIXME:'
+
 {
   description = "a simple yet secure bitcoin node using nix-bitcoin";
 
   inputs = {
     nixpkgs.url = "nixpkgs/nixos-unstable";
     nix-bitcoin.url = "github:fort-nix/nix-bitcoin/release";
+    # You can also use a version branch to track a specific NixOS release
+    # nix-bitcoin.url = "github:fort-nix/nix-bitcoin/nixos-24.05";
   };
 
   outputs = {
@@ -21,16 +30,32 @@
         modules = [
           ./configuration.nix
           nix-bitcoin.nixosModules.default
+          # Optional:
+          # Import the secure-node preset, an opinionated config to enhance security
+          # and privacy.
           (nix-bitcoin + "/modules/presets/secure-node.nix")
           {
             nix-bitcoin = {
+              # Automatically generate all secrets required by services.
+              # The secrets are stored in /etc/nix-bitcoin-secrets
               generateSecrets = true;
+              # When using nix-bitcoin as part of a larger NixOS configuration, set the following to enable
+              # interactive access to nix-bitcoin features (like bitcoin-cli) for your system's main user
               operator = {
                 enable = true;
+                # FIXME: Set this to your system's main user
                 name = "satoshi";
               };
             };
           }
+          # If you use a custom nixpkgs version for evaluating your system
+          # (instead of `nix-bitcoin.inputs.nixpkgs` like in this example),
+          # consider setting `useVersionLockedPkgs = true` to use the exact pkgs
+          # versions for nix-bitcoin services that are tested by nix-bitcoin.
+          # The downsides are increased evaluation times and increased system
+          # closure size.
+          #
+          # nix-bitcoin.useVersionLockedPkgs = true;
         ];
       };
     };