Add Maven Central badge with latest version

Author: felixbarny

README.md

@@ -1,5 +1,6 @@
 [![Build Status](https://travis-ci.org/elastic/apm-agent-java.svg?branch=master)](https://travis-ci.org/elastic/apm-agent-java)
 [![codecov](https://codecov.io/gh/elastic/apm-agent-java/branch/master/graph/badge.svg)](https://codecov.io/gh/elastic/apm-agent-java)
+[![Maven Central](https://maven-badges.herokuapp.com/maven-central/co.elastic.apm/apm-agent-java/badge.svg)](https://maven-badges.herokuapp.com/maven-central/co.elastic.apm/apm-agent-java)
 
 # apm-agent-java
 

docs/intro.asciidoc

@@ -51,11 +51,9 @@ The first step in getting started with the Elastic APM Java agent ist to declare
 compile "co.elastic.apm:apm-agent-java:$elasticApmVersion"
 ----
 
-NOTE: Currently the agent is not yet published to maven central.
-So you have to check out the agent and build it from source.
-To do that,
-simply execute
-`git clone https://github.com/elastic/apm-agent-java.git && cd apm-agent-java && ./mvnw install`.
+Replace the version placeholders with the latest version:
+image:https://maven-badges.herokuapp.com/maven-central/co.elastic.apm/apm-agent-java/badge.svg[
+link=https://maven-badges.herokuapp.com/maven-central/co.elastic.apm/apm-agent-java]
 
 
 To get you off the ground, we've prepared guides for the most popular frameworks: