update README for 2.4.0 release

Author: benoitc

README.md

@@ -3,7 +3,7 @@
 [![Build Status](https://github.com/EnkiMultimedia/erlang-rocksdb/workflows/build/badge.svg)](https://github.com/EnkiMultimedia/erlang-rocksdb/actions?query=workflow%3Abuild)
 [![Hex pm](http://img.shields.io/hexpm/v/rocksdb.svg?style=flat)](https://hex.pm/packages/rocksdb)
 
-**Current version: 2.3.0**
+**Current version: 2.4.0**
 
 Copyright (c) 2016-2026 Benoît Chesneau
 
@@ -25,6 +25,8 @@ Feedback and pull requests welcome! If a particular feature of RocksDB is import
 - Pessimistic transactions with row-level locking
 - Backup support
 - Erlang merge operator
+- Posting list merge operator for inverted indexes
+- Compaction filters (declarative rules and Erlang callbacks)
 - SST file support (write, ingest, read)
 - Customized build support
 - Tested on macOS, FreeBSD, Solaris and Linux