Added link to the project repository of the Git Commit Id Plugin

The documentation currently misses the link to Git Commit Id Plugin,
while offering at the same time a link to the Gradle plugin to
gather Git information.
This pull requests adds the missing link. Readers can now get
more information on the features of the plugin.

spring-boot-project/spring-boot-docs/src/docs/asciidoc/howto/build.adoc

@@ -53,7 +53,7 @@ TIP: See the {spring-boot-gradle-plugin-docs}#integrating-with-actuator-build-in
 Both Maven and Gradle allow generating a `git.properties` file containing information about the state of your `git` source code repository when the project was built.
 
 For Maven users, the `spring-boot-starter-parent` POM includes a pre-configured plugin to generate a `git.properties` file.
-To use it, add the following declaration to your POM:
+To use it, add the following declaration for the https://github.com/git-commit-id/git-commit-id-maven-plugin[`Git Commit Id Plugin`]to your POM:
 
 [source,xml,indent=0,subs="verbatim"]
 ----