config(flake.nix): Specify the Cachix binary cache for this repo

Author: PetarKirov

flake.nix

@@ -1,6 +1,11 @@
 {
   description = "nix-blockchain-development";
 
+  nixConfig = {
+    extra-substituters = "https://nix-blockchain-development.cachix.org";
+    extra-trusted-public-keys = "nix-blockchain-development.cachix.org-1:Ekei3RuW3Se+P/UIo6Q/oAgor/fVhFuuuX5jR8K/cdg=";
+  };
+
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-22.05";
     flake-utils.url = github:numtide/flake-utils;