Add note for maven plugin documentation

Update the reference guide to add a call-out to the new generated
maven plugin site.

Finishes gh-772

spring-boot-docs/src/main/asciidoc/build-tool-plugins.adoc

@@ -15,9 +15,12 @@ unsupported build system. If you are just getting started, you might want to rea
 
 [[build-tool-plugins-maven-plugin]]
 == Spring Boot Maven plugin
-The {mp-root}/[Spring Boot Maven Plugin] provides Spring Boot support in Maven, allowing you to
+The {spring-boot-maven-plugin-site}/[Spring Boot Maven Plugin] provides Spring Boot
-package executable jar or war archives and run an application ``in-place''. To use it you
+support in Maven, allowing you to package executable jar or war archives and run an
-must be using Maven 3 (or better).
+application ``in-place''. To use it you must be using Maven 3 (or better).
+
+NOTE: Refer to the {spring-boot-maven-plugin-site}/[Spring Boot Maven Plugin Site]
+for complete plugin documentation.
 
 
 
@@ -151,7 +154,8 @@ need to mark the embedded container dependencies as ``provided'', e.g:
 	</project>
 ----
 
-Advanced configuration options and examples are available in the {mp-root}/[plugin info page].
+Advanced configuration options and examples are available in the
+{spring-boot-maven-plugin-site}/[plugin info page].
 
 
 

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

@@ -25,7 +25,7 @@ Phillip Webb; Dave Syer; Josh Long; Stéphane Nicoll; Rob Winch; Andy Wilkinson;
 :dc-spring-boot: {dc-root}/org/springframework/boot
 :dc-spring-boot-autoconfigure: {dc-root}/org/springframework/boot/autoconfigure
 :dc-spring-boot-actuator: {dc-root}/org/springframework/boot/actuate
-:mp-root: http://docs.spring.io/spring-boot/docs/{spring-boot-docs-version}/maven-plugin
+:spring-boot-maven-plugin-site: http://docs.spring.io/spring-boot/docs/{spring-boot-docs-version}/maven-plugin
 :spring-reference: http://docs.spring.io/spring/docs/current/spring-framework-reference/htmlsingle
 :spring-security-reference: http://docs.spring.io/spring-security/site/docs/current/reference/htmlsingle
 :spring-javadoc: http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework