Add Java Data Structures resources (#1723)

* Update 104-datastructures.md

Added content in the Java roadmap to learn Data Structures and Algorithms.

* Update content/roadmaps/110-java/content/100-java-fundamentals/104-datastructures.md

Co-authored-by: Kamran Ahmed <kamranahmed.se@gmail.com>

content/roadmaps/110-java/content/100-java-fundamentals/104-datastructures.md

@@ -1 +1,8 @@
-# Datastructures
+# Datastructures
+
+As the name indicates itself, a **Data Structure** is a way of organizing the data in the **memory** so that it can be used efficiently. Some common data structures are array, linked list, stack, hashtable, queue, tree, heap, and graph.
+
+<ResourceGroupTitle>Free Content</ResourceGroupTitle>
+<BadgeLink colorScheme='yellow' badgeText='Read' href='https://www.geeksforgeeks.org/data-structures'>What are Data Structures?</BadgeLink>
+<BadgeLink colorScheme='yellow' badgeText='Read' href='https://www.javatpoint.com/data-structure-tutorial'> Data Structures and Algorithms</BadgeLink>
+<BadgeLink badgeText='Watch' href='https://www.coursera.org/learn/data-structures'>Data Structures and Algorithms</BadgeLink>