Add an example using injected credentials

Author: shpsec-blaisep

pipeline-examples/push-git-repo/README.md

@@ -1,15 +1,21 @@
 # Synopsis
 
 This demonstrates how to push a tag (or branch, etc) to a remote Git
-repository from within a Pipeline job. Currently it only contains an
-example for pushing using username and password to authenticate.
+repository from within a Pipeline job. The authentication step may vary between projects. This example illustrates injected credentials and also username / password authentication.
 
 # Note
 
+If you inject a credential associated with your Git repo, use the Snippet Generator to select the plain `Git` option and it will return a snippet with this gem:
+
+```java
+stage('Checkout') {
+       git branch: 'lts-1.532', credentialsId: '82aa2d26-ef4b-4a6a-a05f-2e1090b9ce17', url: '[email protected]:jenkinsci/maven-plugin.git'
+   }
+```
 This is not ideal - there is an open JIRA,
-https://issues.jenkins-ci.org/browse/JENKINS-28335, for getting the
-GitPublisher Jenkins functionality working with Pipeline.
+https://issues.jenkins-ci.org/browse/JENKINS-28335, for getting the GitPublisher Jenkins functionality working with Pipeline.
 
 # Credit
 
 Based on Stackoverflow answer at http://stackoverflow.com/questions/33570075/tag-a-repo-from-a-jenkins-workflow-script
+Injected credentials gist at https://gist.github.com/blaisep/eb8aa720b06eff4f095e4b64326961b5#file-jenkins-pipeline-git-cred-md