updated README.md and index.md

Author: Ghruank

Theory/index.md

@@ -10,11 +10,11 @@ Welcome to **DSA's Theory**, this very directory serves as a treasure trove of w
   - [Complexity Analysis](./Complexity-Analysis/README.md)
 
 - **Data Structures**
-  - [Graphs](./Data-Structures/Graphs/README.md)
-  - [Linked Lists](./Data-Structures/Linked-Lists/README.md)
-  - [Queues](./Data-Structures/Queues/README.md)
   - [Stacks](./Data-Structures/Stacks/README.md)
+  - [Queues](./Data-Structures/Queues/README.md)
+  - [Linked Lists](./Data-Structures/Linked-Lists/README.md)
   - [Trees](./Data-Structures/Trees/README.md)
+  - [Graphs](./Data-Structures/Graphs/README.md)
 <!-- TABLE OF CONTENT ENDS -->
 
 # Table of Contribution