Added changelog for new 1.0.24 release

Author: micdah

CHANGELOG.md

@@ -1,5 +1,23 @@
 # Changelog
 
+## 1.0.24
+
+* Added support for attachment link buttons (_type of attachment action_) which opens a provided URL if clicked,
+  allowing you to add up to 5 buttons to each attachment.
+  See [Attaching buttons to messages](https://api.slack.com/docs/message-attachments#attaching_buttons_to_messages)
+  for more.
+  
+  Example:
+    ```cs
+    await new client.SendAsync(b => b
+        .WithText("Look at my buttons")
+        .WithAttachment(a => a
+            .WithTitle("Now with actions")
+            .WithText("...which are pretty neat")
+            .WithLinkButtonAction("Click me", "http://google.com", ActionStyle.Primary)
+            .WithLinkButtonAction("Don't click me", "http://bing.com", ActionStyle.Danger)));
+    ``` 
+
 ## 1.0.23
 
-First documented release with initial features provided by the Slack Webhook API
+* First documented release with initial features provided by the Slack Webhook API