More details in readme.md (jcenter repo)

README.md

@@ -14,12 +14,16 @@ Common example of how to generate the client code and use it in your project:
 1. Generate Petstore dropwizard client
 2. Make java classes depend on generated sources
 
-```build.gradle 
+```build.gradle
 plugins {
     id('java')
     id('com.twilio.guardrail.gradle.plugin')
 }
 
+repositories {
+    jcenter()
+}
+
 dependencies {
     ... // insert corresponding dependencies to compile
 }