Added groups for commands in help

[KeerthanaAP]

Fix for #347

Added groups for commands in help

./pvsadm help               
I0314 21:28:53.205226   35870 root.go:50] Using an API key from IBMCLOUD_API_KEY environment variable
Power Systems Virtual Server projects deliver flexible compute capacity for Power Systems workloads.
Integrated with the IBM Cloud platform for on-demand provisioning.

This is a tool built for the Power Systems Virtual Server helps managing and maintaining the resources easily

Usage:
  pvsadm [command]

Resource Management Commands:
  create      Create the resources
  delete      Delete the resources
  get         Get the resources
  purge       Purge the powervs resources

DHCP Commands:
  dhcp-sync   dhcp-sync command
  dhcpserver  dhcpserver command

Image Commands:
  image       PowerVS Image management

Administration Commands:
  completion  Generate the autocompletion script for the specified shell
  help        Help about any command
  version     Print the version number

[mkumatag]

/lgtm

[ppc64le-cloud-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: KeerthanaAP, mkumatag

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [mkumatag]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment