Improve links to Gradle plugin's documentation

Closes gh-9386

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

@@ -164,11 +164,14 @@ Advanced configuration options and examples are available in the
 
 [[build-tool-plugins-gradle-plugin]]
 == Spring Boot Gradle plugin
-The {spring-boot-gradle-plugin}[Spring Boot Gradle Plugin] provides Spring Boot support
-in Gradle, allowing you to package executable jar or war archives, run Spring Boot
-applications and use the dependency management provided by `spring-boot-dependencies`.
-It requires Gradle 3.4 or later. Please refer to the {spring-boot-gradle-plugin}[plugin's
-documentation] to learn more.
+The Spring Boot Gradle Plugin provides Spring Boot support in Gradle, allowing you to
+package executable jar or war archives, run Spring Boot applications and use the
+dependency management provided by `spring-boot-dependencies`. It requires Gradle 3.4 or
+later. Please refer to the plugin's documentation to learn more:
+
+* Reference ({spring-boot-gradle-plugin}/reference/html[HTML] and
+  {spring-boot-gradle-plugin}/reference/pdf/spring-boot-gradle-plugin-reference.pdf[PDF])
+* {spring-boot-gradle-plugin}/api[API]
 
 
 

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

@@ -42,7 +42,7 @@ The curated list contains all the spring modules that you can use with Spring Bo
 well as a refined list of third party libraries. The list is available as a standard
 <<using-boot-maven-without-a-parent,Bills of Materials (`spring-boot-dependencies`)>>
 that can be used with both <<using-boot-maven-parent-pom,Maven>> and
-{spring-boot-gradle-plugin}[Gradle].
+<<using-boot-gradle,Gradle>>.
 
 WARNING: Each release of Spring Boot is associated with a base version of the Spring
 Framework so we **highly** recommend you to not specify its version on your own.
@@ -194,10 +194,12 @@ the parent.
 
 [[using-boot-gradle]]
 === Gradle
-To learn about using Spring Boot with Gradle, please refer to the
-{spring-boot-gradle-plugin}[documentation for Spring Boot's Gradle plugin].
-
+To learn about using Spring Boot with Gradle, please refer to the documentation for
+Spring Boot's Gradle plugin:
 
+* Reference ({spring-boot-gradle-plugin}/reference/html[HTML] and
+  {spring-boot-gradle-plugin}/reference/pdf/spring-boot-gradle-plugin-reference.pdf[PDF])
+* {spring-boot-gradle-plugin}/api[API]
 
 [[using-boot-ant]]
 ===  Ant