Explain Bloom filter in README

Author: korthaj

README.md

@@ -1,6 +1,10 @@
 # Your basic Bloom filter
 
-Golang Bloom filter implementation
+### Golang probabilistic set data structure
+
+A Bloom filter is a fast and space-efficient probabilistic data structure
+used to test set membership. A membership test returns either ”likely member”
+or ”definitely not a member”
 
 ![Neutral density filter](ND-filter.jpg)