New doc theme (#387)

docs/src/Shortcodes/AlertShortcode.cs

@@ -0,0 +1,15 @@
+using System.Collections.Generic;
+using Statiq.Common;
+using System.Xml.Linq;
+
+namespace Docs.Shortcodes
+{
+    public class AlertShortcode : SyncShortcode
+    {
+        public override ShortcodeResult Execute(KeyValuePair<string, string>[] args, string content, IDocument document, IExecutionContext context)
+        {
+
+            return $"<div class=\"alert-warning\">{content}</div>";
+        }
+    }
+}