nix: advertise binary cache for flake users

Cachix is no longer needed to be installed by users, because flakes
can now set binary caches.

Author: vlaci

docs/installation.md

@@ -75,14 +75,16 @@ The Nix derivation installs all 3rd party dependencies.
           experimental-features = nix-command flakes
           EOF
 
-1.  _Optional_: use pre-built binaries from GitHub using [cachix](https://app.cachix.org/cache/unblob):
-
-        nix-env -iA cachix -f https://cachix.org/api/v1/install
-        cachix use unblob
-
 1.  Install unblob:
 
-        nix profile install github:onekey-sec/unblob
+        $ nix profile install github:onekey-sec/unblob
+        do you want to allow configuration setting 'extra-substituters' to be set to 'https://unblob.cachix.org' (y/N)? y
+        do you want to permanently mark this value as trusted (y/N)? y
+        do you want to allow configuration setting 'extra-trusted-public-keys' to be set to
+        'unblob.cachix.org-1:5kWA6DwOg176rSqU8TOTBXWxsDB4LoCMfGfTgL5qCAE=' (y/N)? y
+        do you want to permanently mark this value as trusted (y/N)? y
+
+    Using and trusting substituter (binary cache) and its public key is optional but greatly speeds up installation.
 
 - Check that everything works correctly:
 

flake.nix

@@ -20,6 +20,13 @@
     flake = false;
   };
 
+  nixConfig = {
+    extra-substituters = [ "https://unblob.cachix.org" ];
+    extra-trusted-public-keys = [
+      "unblob.cachix.org-1:5kWA6DwOg176rSqU8TOTBXWxsDB4LoCMfGfTgL5qCAE="
+    ];
+  };
+
   outputs = { self, nixpkgs, filter, unblob-native, pyperscan, sasquatch, ... }:
     let
       # System types to support.