Added WakaTime badge

Author: devgianlu

README.md

@@ -1,6 +1,7 @@
 # librespot-java
 [![Build Status](https://travis-ci.com/librespot-org/librespot-java.svg?branch=dev)](https://travis-ci.com/librespot-org/librespot-java)
 [![Codacy Badge](https://api.codacy.com/project/badge/Grade/1ec8ca04e5054558a089bc7f640079a6)](https://www.codacy.com/manual/devgianlu/librespot-java?utm_source=github.com&utm_medium=referral&utm_content=librespot-org/librespot-java&utm_campaign=Badge_Grade)
+[![time tracker](https://wakatime.com/badge/github/librespot-org/librespot-java.svg)](https://wakatime.com/badge/github/librespot-org/librespot-java)
 [![Maven Central](https://maven-badges.herokuapp.com/maven-central/xyz.gianlu.librespot/librespot-java/badge.svg)](https://maven-badges.herokuapp.com/maven-central/xyz.gianlu.librespot/librespot-java)
 
 `librespot-java` is a port of [librespot](https://github.com/librespot-org/librespot), originally written in Rust, which has evolved into the most up-to-date open-source Spotify client. Additionally, this implementation provides a useful API to request metadata or control the player, more [here](api).