Add xorfilter

Adapted from nrdmn#20

Author: catdevnull

readme.md

@@ -13,6 +13,7 @@
 - [Sahnvour/zig-containers](https://github.com/Sahnvour/zig-containers) - A container library for Zig.
 - [Srekel/zig-sparse-set](https://github.com/Srekel/zig-sparse-set) - Sparse sets for zig, supporting both SOA and AOS style
 - [v1zix/zig-string](https://github.com/v1zix/zig-string) - Strings for Zig
+- [hexops/xorfilter](https://github.com/hexops/xorfilter) - Xor Filters for checking if a key is part of a set.
 
 ## Allocators and memory
 - [dbandstra/zig-hunk](https://github.com/dbandstra/zig-hunk) - Basic stack allocator for Zig