chore: user real example, and fix yaml in markdown

Author: alexeldeib

docs/book/src/cronjob-tutorial/running.md

@@ -25,7 +25,9 @@ anything just yet.
 At this point, we need a CronJob to test with.  Let's write a sample to
 `config/samples/batch_v1_cronjob.yaml`, and use that:
 
+```yaml
 {{#include ./testdata/project/config/samples/batch_v1_cronjob.yaml}}
+```
 
 ```bash
 kubectl create -f config/samples/batch_v1_cronjob.yaml

docs/book/src/cronjob-tutorial/testdata/project/config/samples/batch_v1_cronjob.yaml

@@ -3,5 +3,18 @@ kind: CronJob
 metadata:
   name: cronjob-sample
 spec:
-  # Add fields here
-  foo: bar
+  schedule: "*/1 * * * *"
+  startingDeadlineSeconds: 60
+  concurrencyPolicy: Allow # explicitly specify, but Allow is also default.
+  jobTemplate:
+    spec:
+      template:
+        spec:
+          containers:
+          - name: hello
+            image: busybox
+            args:
+            - /bin/sh
+            - -c
+            - date; echo Hello from the Kubernetes cluster
+          restartPolicy: OnFailure