Update readme (#16)

* Updated readme

Author: xzeck

README.md

@@ -2,6 +2,16 @@
 
 This is a rust implementation of [Google's HyperLogLog](https://static.googleusercontent.com/media/research.google.com/en//pubs/archive/40671.pdf) algorithm
 
+## Features
+
+- [x] Support for primitive data types
+- [x] Support for custom data types
+- [x] Pluggable hasher
+- [x] Save state
+- [x] Load state
+
+
+
 Usage:
 
 ```rust