add colored headlines for markdown

after/plugin/headlines.lua

@@ -12,6 +12,16 @@ headlines.setup {
       "@neorg.headings.4.title",
       "@neorg.headings.5.title",
       "@neorg.headings.6.title"
-    },
+    }
+  },
+  markdown = {
+    headline_highlights = {
+      "@neorg.headings.1.title",
+      "@neorg.headings.2.title",
+      "@neorg.headings.3.title",
+      "@neorg.headings.4.title",
+      "@neorg.headings.5.title",
+      "@neorg.headings.6.title"
+    }
   },
 }