Fix maven repo references in README

Closes gh-27

Author: philwebb

README.adoc

@@ -34,6 +34,38 @@ You can use the https://github.com/asciidoctor/asciidoctor-maven-plugin[Asciidoc
 </plugin>
 ----
 
+You will probably also need to add the Spring Maven repository:
+
+[source,xml]
+----
+<repositories>
+	<repository>
+		<id>spring-release</id>
+		<name>Spring Releases</name>
+		<url>https://repo.spring.io/release</url>
+		<snapshots>
+			<enabled>false</enabled>
+		</snapshots>
+	</repository>
+</repositories>
+----
+
+or for milestones:
+
+[source,xml]
+----
+<repositories>
+	<repository>
+		<id>spring-milestones</id>
+		<name>Spring Milestones</name>
+		<url>https://repo.spring.io/milestone</url>
+		<snapshots>
+			<enabled>false</enabled>
+		</snapshots>
+	</repository>
+</repositories>
+----
+
 
 
 == Gradle build integration
@@ -45,13 +77,6 @@ plugins {
 	id 'org.asciidoctor.jvm.convert' version '3.1.0'
 }
 
-repositories {
-	mavenCentral()
-	maven {
-		url "https://repo.spring.io/release"
-	}
-}
-
 configurations {
 	asciidoctorExtensions
 }
@@ -69,6 +94,30 @@ asciidoctor {
 }
 ----
 
+You will probably also need to add the Spring Maven repository:
+
+[source,gradle]
+----
+repositories {
+	mavenCentral()
+	maven {
+		url "https://repo.spring.io/release"
+	}
+}
+----
+
+or for milestones:
+
+[source,gradle]
+----
+repositories {
+	mavenCentral()
+	maven {
+		url "https://repo.spring.io/milestone"
+	}
+}
+----
+
 
 
 == Features