Update README.md

Author: lemire

README.md

@@ -6,6 +6,10 @@ This is a research library currently. It is not meant for production use.
 
 Developers might want to consider our [Header-only Xor Filter library in C](https://github.com/FastFilter/xor_singleheader/).
 
+Reference: [Xor Filters: Faster and Smaller Than Bloom and Cuckoo Filters](https://arxiv.org/abs/1912.08258), Journal of Experimental Algorithmics (to appear).
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 ## Prerequisites
 
 - A  C++11 compiler such as GNU G++ or LLVM Clang++