Fix reference to Spring Initializr doc

Closes gh-13906

Author: snicoll

spring-boot-docs/src/main/asciidoc/getting-started.adoc

@@ -462,8 +462,8 @@ that use Spring Boot. If you're looking to solve a specific problem; check there
 You can shortcut the steps below by going to https://start.spring.io and choosing the
 `web` starter from the dependencies searcher. This will automatically generate a new
 project structure so that you can <<getting-started-first-application-code,start coding
-right away>>. Check the https://github.com/spring-io/initializr[documentation for
-more details].
+right away>>. Check the {spring-initializr-reference}/#user-guide[documentation for more
+details].
 ====
 
 Before we begin, open a terminal to check that you have valid versions of Java and Maven

spring-boot-docs/src/main/asciidoc/index.adoc

@@ -35,6 +35,7 @@ Phillip Webb; Dave Syer; Josh Long; Stéphane Nicoll; Rob Winch; Andy Wilkinson;
 :dependency-management-plugin: https://github.com/spring-gradle-plugins/dependency-management-plugin
 :dependency-management-plugin-documentation: {dependency-management-plugin}/blob/master/README.md
 :spring-boot-maven-plugin-site: http://docs.spring.io/spring-boot/docs/{spring-boot-docs-version}/maven-plugin
+:spring-initializr-reference: https://docs.spring.io/initializr/docs/current/reference/htmlsingle
 :spring-reference: http://docs.spring.io/spring/docs/{spring-docs-version}/spring-framework-reference/htmlsingle
 :spring-security-reference: http://docs.spring.io/spring-security/site/docs/{spring-security-docs-version}/reference/htmlsingle
 :spring-security-oauth2-reference: http://projects.spring.io/spring-security-oauth/docs/oauth2.html