Store keys in pem file

Change-Id: I6b6e7238df5690894fab32da27af1a5e4de08966
diff --git a/single-master/README.md b/single-master/README.md
index d444943..7d3766d 100644
--- a/single-master/README.md
+++ b/single-master/README.md
@@ -49,7 +49,8 @@
 * Create a key pair to access the EC2 instances in the cluster:
 
 ```
-aws ec2 create-key-pair --key-name gerrit-cluster-keys
+aws ec2 create-key-pair --key-name gerrit-cluster-keys \
+  --query 'KeyMaterial' --output text > gerrit-cluster.pem
 ```
 
 *NOTE: the EC2 key pair are useful when you need to connect to the EC2 instances