Add RuntimeResult demo

docs/guides/commands/post-execution.md

@@ -93,6 +93,10 @@ Here's an example of a command that utilizes such logic:
 
 [!code[Usage](samples/customresult_usage.cs)]
 
+And now we can check for it in our [CommandExecuted] handler:
+
+[!code[Usage](samples/command_executed_adv_demo.cs)]
+
 ## CommandService.Log Event
 
 We have so far covered the handling of various result types, but we

docs/guides/commands/samples/command_executed_adv_demo.cs

@@ -0,0 +1,13 @@
+public async Task OnCommandExecutedAsync(CommandInfo command, ICommandContext context, IResult result)
+{
+    switch(result)
+    {
+        case MyCustomResult customResult:
+            // do something extra with it
+            break;
+        default:
+            if (!string.IsNullOrEmpty(result.ErrorReason))
+                await context.Channel.SendMessageAsync(result.ErrorReason);
+            break;
+    }
+}