Update README.markdown

Author: scalls

Radix-Tree/README.markdown

@@ -1,3 +1,7 @@
 # Radix Tree
 
 A radix tree (or radix trie, compact prefix tree) is a space-optimized tree used for constructing associative arrays that are usually expressed as strings. Edges in radix trees store strings. If you started at the root of the tree and traversed down to any node that has no children, concatenating the edges in order of traversal would result in a stored word. An example can be seen [here](https://en.wikipedia.org/wiki/Radix_tree#/media/File:Patricia_trie.svg).
+
+## Operations
+
+Typical operations on a radix tree include lookup, insertion, deletion, find predecessor, find successor, and find all strings with common prefix. The running time of lookup, insertion, and deletion is O(k) where k is the length of the key. This is different from most trees because these operations usually run in O(logn) time where n is the number of nodes in the tree.