Replace Bookmarks card with Window Sync card

Signed-off-by: mr. m <[email protected]>

Author: mr-cheffy

content/docs/user-manual/index.mdx

@@ -46,9 +46,9 @@ Welcome to the Zen Browser User Manual! This guide is designed to provide you wi
     href="/user-manual/split-view"
   />
   <Card 
-    title="Bookmarks" 
-    description="Managing bookmarks in Zen"
-    href="/user-manual/bookmarks"
+    title="Window Sync" 
+    description="Your opened windows mirror with each other instantly"
+    href="/user-manual/window-sync"
   />
   <Card 
     title="Picture-in-Picture"