add tag in pages and groups

Author: dks333

navigation.mdx

@@ -79,6 +79,7 @@ Groups allow you to group your pages. Groups can also be nested within each othe
       },
       {
         "group": "Writing Content",
+        "tag": "NEW",
         "pages": ["writing-content/page", "writing-content/text"]
       }
     ]

pages.mdx

@@ -58,6 +58,16 @@ iconType: "solid"
 ---
 ```
 
+## Tag
+
+You can set a tag for your page. This is useful to categorize your pages and make them easier to find.
+
+```jsx
+---
+tag: "NEW"
+---
+```
+
 ## API Pages
 
 API pages let you build interactive API playgrounds. To create an API page, you