doc: add note about maven central

Author: suniala

README.md

@@ -27,6 +27,10 @@ void printTimeSignature(MidiTimeSignatureM m) {
 }
 ```
 
+## Usage
+
+Get it from Maven Central: https://central.sonatype.com/artifact/io.github.suniala/java-midi-decoder
+
 ## Related Projects
 * https://github.com/suniala/midi-tuutti uses this library
 * http://www.jfugue.org enables "Music Programming for Java™ and JVM Languages"