clone repo in Jenkinsfile

Jenkinsfile

@@ -1,10 +1,20 @@
 pipeline {
     agent any 
     stages {
-        stage('Stage 1') {
+        stage('Hello') {
             steps {
                 echo 'Hello world!' 
             }
         }
+        stage('Checkout') {
+            steps {
+                script {
+                    git credentialsId: 's444498', url: 'https://git.wmi.amu.edu.pl/s444498/ium_444498.git'
+                    sh "ls -lart ./*"
+                    sh "git branch -a"
+                    sh "git checkout master"
+                }
+            }
+        }
     }
 }