Add --preemptible flag while creating instance

Separate command is added to create instance with --preemptible flag which cost lesser
but it will be shutdown automatically within 24 hrs.

docs/03-compute-resources.md

@@ -114,6 +114,24 @@ for i in 0 1 2; do
 done
 ```
 
+__Use following command to create preemptible instance, which costs lower but it will be shutdown automtically within 24 hours__. 
+```
+for i in 0 1 2; do
+  gcloud compute instances create controller-${i} \
+    --async \
+    --boot-disk-size 200GB \
+    --can-ip-forward \
+    --image-family ubuntu-1804-lts \
+    --image-project ubuntu-os-cloud \
+    --machine-type n1-standard-1 \
+    --private-network-ip 10.240.0.1${i} \
+    --scopes compute-rw,storage-ro,service-management,service-control,logging-write,monitoring \
+    --subnet kubernetes \
+    --tags kubernetes-the-hard-way,controller \ 
+    --preemptible
+done
+```
+
 ### Kubernetes Workers
 
 Each worker instance requires a pod subnet allocation from the Kubernetes cluster CIDR range. The pod subnet allocation will be used to configure container networking in a later exercise. The `pod-cidr` instance metadata will be used to expose pod subnet allocations to compute instances at runtime.
@@ -139,6 +157,26 @@ for i in 0 1 2; do
 done
 ```
 
+__Use following command to create preemptible instance, which costs lower but it will be shutdown automtically within 24 hours__. 
+```
+for i in 0 1 2; do
+  gcloud compute instances create worker-${i} \
+    --async \
+    --boot-disk-size 200GB \
+    --can-ip-forward \
+    --image-family ubuntu-1804-lts \
+    --image-project ubuntu-os-cloud \
+    --machine-type n1-standard-1 \
+    --metadata pod-cidr=10.200.${i}.0/24 \
+    --private-network-ip 10.240.0.2${i} \
+    --scopes compute-rw,storage-ro,service-management,service-control,logging-write,monitoring \
+    --subnet kubernetes \
+    --tags kubernetes-the-hard-way,worker \ 
+    --preemptible
+done
+```
+
+
 ### Verification
 
 List the compute instances in your default compute zone: