Fixed readme
Change-Id: Idb0a05fef17127419f71027b26c9f0e8daf549b2
diff --git a/lib/Krawfish/Index/Fields/Rank.pm b/lib/Krawfish/Index/Fields/Rank.pm
index 4d3116a..6821826 100644
--- a/lib/Krawfish/Index/Fields/Rank.pm
+++ b/lib/Krawfish/Index/Fields/Rank.pm
@@ -24,7 +24,9 @@
# https://github.com/gpakosz/PackedArray
# That's why max_rank is important, because it indicates
# how many bits per doc are necessary to encode
-# the rank!
+# the rank ceil(log(N)/log(2))!
+# https://arxiv.org/pdf/1401.6399.pdf
+# https://github.com/zhenjl/encoding
# TODO:
# In case, a field is only set for a couple of documents, a different