Added feature table

Author: Nyholm

README.md

@@ -1,4 +1,11 @@
 # Void PSR-6 adapter 
 [![Build Status](https://travis-ci.org/php-cache/void-adapter.svg?branch=master)](https://travis-ci.org/php-cache/void-adapter) [![codecov.io](https://codecov.io/github/php-cache/void-adapter/coverage.svg?branch=master)](https://codecov.io/github/php-cache/void-adapter?branch=master)
 
-This is a implementation for the PSR-6 for Void cache. This implementation supports tags. 
+This is a void implementation of PSR-6. Other names for this adapter could be Blackhole or Null. This 
+adapter does not save anything and will always return an empty CacheItem. 
+
+| Feature |   |
+| ------- | - | 
+| Flush everything | No 
+| Expiration time | No
+| Support for tags | No