Adding README

Author: armon

���README.md

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+go-radix [![Build Status](https://travis-ci.org/armon/radix.png)](https://travis-ci.org/armon/radix)
+=========
+
+Provides the `radix` package that implements a [radix tree](http://en.wikipedia.org/wiki/Radix_tree).
+The package only provides a single `Tree` implementation, optimized for sparse nodes.
+
+As a radix tree, it provides the following:
+ * O(k) operations. In many cases, this can be faster than a hash table since
+   the hash function is an O(k) operation, and hash tables have very poor cache locality.
+ * Minimum / Maximum value lookups
+ * Ordered iteration
+
+Example
+=======
+
+Below is a simple example of usage
+
+```go
+// Create a tree
+r := radix.New()
+r.Insert("foo", 1)
+r.Insert("bar", 2)
+r.Insert("foobar", 2)
+
+// Find the longest prefix match
+m, _, _ := r.LongestPrefix("foozip")
+if m != "foo" {
+    panic("should be foo")
+}
+```
+