Add lists and keys docs

content/roadmaps/103-react/content/100-react-fundamental-topics/106-lists-and-keys.md

@@ -1 +1,6 @@
-# Lists and keys
+# Lists and Keys
+
+When you render lists in React, you can use the `key` prop to specify a unique key for each item. This key is used to identify which item to update when you want to update a specific item.
+
+<ResourceGroupTitle>Free Content</ResourceGroupTitle>
+<BadgeLink colorScheme='blue' badgeText='Official Docs' href='https://reactjs.org/docs/lists-and-keys.html'>Lists and Keys</BadgeLink>