Added lazy propagation to main README.

Author: kelvinlauKL

README.markdown

@@ -156,6 +156,7 @@ Most of the time using just the built-in `Array`, `Dictionary`, and `Set` types
 - [Splay Tree](Splay%20Tree/). A self balancing binary search tree that enables fast retrieval of recently updated elements.
 - [Threaded Binary Tree](Threaded%20Binary%20Tree/). A binary tree that maintains a few extra variables for cheap and fast in-order traversals.
 - [Segment Tree](Segment%20Tree/). Can quickly compute a function over a portion of an array.
+  - [Lazy Propagation](https://github.com/raywenderlich/swift-algorithm-club/tree/master/Segment%20Tree/LazyPropagation) 
 - kd-Tree
 - [Heap](Heap/). A binary tree stored in an array, so it doesn't use pointers. Makes a great priority queue.
 - Fibonacci Heap