Add a sample for getting the Guild from an IMessage

some users were having trouble with this

docs/guides/samples.md

@@ -17,4 +17,8 @@ title: Samples
 
 #### Sending a message to a channel
 
-[!code-csharp[Message to Channel](samples/faq/send_message.cs)]
+[!code-csharp[Message to Channel](samples/faq/send_message.cs)]
+
+#### Retrieving an IGuild from an IMessage
+
+[!code-csharp[Message to Guild](samples/faq/guild_from_message.cs)]

docs/guides/samples/faq/guild_from_message.cs

@@ -0,0 +1,4 @@
+public async Task MessageReceived(IMessage msg)
+{
+    var guild = (msg.Channel as IGuildChannel)?.Guild;
+}