Adds Caching paper on 2Q algorithm

The algorithm was referenced in an article about
improving buffer cache replacement in OpenBSD.

http://www.tedunangst.com/flak/post/2Q-buffer-cache-algorithm

The article was found on the vldb.org website via a google
search.

http://www.vldb.org/conf/1994/P439.PDF

caching/README.md

@@ -1 +1,3 @@
 [An O(1) algorithm for implementing the LFU cache eviction scheme](https://github.com/papers-we-love/papers-we-love/blob/master/caching/a-constant-algorithm-for-implementing-the-lfu-cache-eviction-scheme.pdf) by Prof. Ketan Shah, Anirban Mitra, Dhruv Matani
+
+[2Q: A Low Overhead High Performance Buffer Management Replacement Algorithm](https://github.com/papers-we-love/papers-we-love/blob/master/caching/2q-a-low-overhead-high-performance-buffer-management-replacement-algorithm.pdf) by Theodore Johnson and Dennis Shasha