Show a nicer error if the config file doesn't exist

src/FakeRelay.Core/Config.cs

@@ -30,6 +30,11 @@ public class Config
             return;
         }
 
+        if (!File.Exists(path))
+        {
+            throw new Exception("Config file does not exist. Run the config command to create it.");
+        }
+
         var data = JSON.Deserialize<ConfigData>(File.ReadAllText(path));
         if (data.PublicKey == null || data.PrivateKey == null || data.Host == null)
         {

src/FakeRelay.Web/Program.cs

@@ -1,10 +1,6 @@
 using FakeRelay.Core;
 using FakeRelay.Web.Services;
-using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.HttpOverrides;
-using Microsoft.Extensions.Configuration;
-using Microsoft.Extensions.DependencyInjection;
-using Microsoft.Extensions.Hosting;
 
 var builder = WebApplication.CreateBuilder(args);
 Config.Init(builder.Configuration.GetValue<string>("CONFIG_PATH"));