Add links to documentation to the pipeline elements.

Jenkinsfile

@@ -31,19 +31,22 @@ echo "Use settings file at ${maven_settings_file}"
 echo "Use local repo at ${maven_local_repo_path}"
 
 pipeline {
+   // see https://jenkins.io/doc/book/pipeline/syntax/#agent
    agent any
 
-   // environment variables available to the Pipeline
+   // see https://jenkins.io/doc/book/pipeline/syntax/#environment
    environment {
       JOB_OPTIONS = "${options}"
    }
 
+   // see https://jenkins.io/doc/book/pipeline/syntax/#parameters
    parameters {
         choice(choices: ['SNAPSHOT-DRY-RUN', 'SNAPSHOT', 'RELEASE-DRY-RUN', 'RELEASE'],
                 description: 'The type of artifacts the build is expected to generate',
                 name: 'Type')
     }
     
+    //see https://jenkins.io/doc/book/pipeline/syntax/#stages
     stages {
         stage('clean up before starting') {
             script {