Revise post-execution docs

* Fix incorrect Optional<T> usage
* Indent some sample code and add a comment reminding the user that the post-execution basic sample code is not ideal.

docs/guides/commands/samples/post-execution/command_executed_demo.cs

@@ -20,15 +20,19 @@ public async Task OnCommandExecutedAsync(Optional<CommandInfo> command, ICommand
 
     // ...or even log the result (the method used should fit into
     // your existing log handler)
-    var commandName = command.HasValue ? command.Name : "A command";
-    await _log.LogAsync(new LogMessage(LogSeverity.Info, "CommandExecution", $"{commandName} was executed at {DateTime.UtcNow}."));
+    var commandName = command.IsSpecified ? command.Value.Name : "A command";
+    await _log.LogAsync(new LogMessage(LogSeverity.Info, 
+        "CommandExecution", 
+        $"{commandName} was executed at {DateTime.UtcNow}."));
 }
 public async Task HandleCommandAsync(SocketMessage msg)
 {
     var message = messageParam as SocketUserMessage;
     if (message == null) return;
     int argPos = 0;
-    if (!(message.HasCharPrefix('!', ref argPos) || message.HasMentionPrefix(_client.CurrentUser, ref argPos)) || message.Author.IsBot) return;
+    if (!(message.HasCharPrefix('!', ref argPos) || 
+        message.HasMentionPrefix(_client.CurrentUser, ref argPos)) || 
+        message.Author.IsBot) return;
     var context = new SocketCommandContext(_client, message);
     await _commands.ExecuteAsync(context, argPos, _services);
 }

docs/guides/commands/samples/post-execution/post-execution_basic.cs

@@ -1,11 +1,14 @@
+// Bad code!!!
 var result = await _commands.ExecuteAsync(context, argPos, _services);
 if (result.CommandError != null)
 	switch(result.CommandError)
 	{
 		case CommandError.BadArgCount:
-			await context.Channel.SendMessageAsync("Parameter count does not match any command's.");
+			await context.Channel.SendMessageAsync(
+				"Parameter count does not match any command's.");
 			break;
 		default:
-			await context.Channel.SendMessageAsync($"An error has occurred {result.ErrorReason}");
+			await context.Channel.SendMessageAsync(
+				$"An error has occurred {result.ErrorReason}");
 			break;
 	}