Update prerequisites.md (#798)

I did not find --instance-id in the tool, it appears there is a --pvs-instance-id instead

Signed-off-by: Paul Bastide <[email protected]>

Author: prb112

docs/book/src/topics/powervs/prerequisites.md

@@ -59,12 +59,12 @@ A public network is required for your kubernetes cluster. Perform the following
 
 ```shell
 $ export IBMCLOUD_API_KEY=<API_KEY>
-$ pvsadm image import --instance-id <SERVICE_INSTANCE_ID> -b <BUCKETNAME> --object <OBJECT> --pvs-image-name <POWERVS_IMAGE_NAME> --bucket-region <REGION> --public-bucket
+$ pvsadm image import --pvs-instance-id <SERVICE_INSTANCE_ID> -b <BUCKETNAME> --object <OBJECT> --pvs-image-name <POWERVS_IMAGE_NAME> --bucket-region <REGION> --public-bucket
 ```
 
 e.g:
 ```shell
-$ pvsadm image import --instance-id 6d892c30-5387-4685-85d0-4999d9c22a8c -b power-oss-bucket --object capibm-powervs-centos-streams8-1-24-2.ova.gz --pvs-image-name capibm-powervs-centos-streams8-1-24-2 --bucket-region us-south --public-bucket
+$ pvsadm image import --pvs-instance-id 6d892c30-5387-4685-85d0-4999d9c22a8c -b power-oss-bucket --object capibm-powervs-centos-streams8-1-24-2.ova.gz --pvs-image-name capibm-powervs-centos-streams8-1-24-2 --bucket-region us-south --public-bucket
 ```
 
-For more information about the images can be found at [machine-images](../../machine-images/powervs.md) section
+For more information about the images can be found at [machine-images](../../machine-images/powervs.md) section