Add comodal/hash-overlay implementation to README.

Author: jpe42

README.md

@@ -80,7 +80,9 @@ Yes, but we already have to agree on functions, so this is not hard. The table e
 ## Implementations:
 
 - [go-multihash](//github.com/multiformats/go-multihash)
-- [java-multihash](//github.com/multiformats/java-multihash)
+- java-multihash
+  - [multiformats/java-multihash](//github.com/multiformats/java-multihash)
+  - [comodal/hash-overlay](//github.com/comodal/hash-overlay)
 - [js-multihash](//github.com/multiformats/js-multihash)
 - [clj-multihash](//github.com/multiformats/clj-multihash)
 - rust-multihash