Update the cmd to support MPI operator in ReadME

[denkensk]

Signed-off-by: Alex Wang wangqingcan1990@gmail.com

What this PR does / why we need it:
Update the cmd to support MPI operator

Which issue(s) this PR fixes (optional, in Fixes #<issue number>, #<issue number>, ... format, will close the issue(s) when PR gets merged):
Fixes #

Checklist:

• Docs included if any changes are user facing

[coveralls]

Pull Request Test Coverage Report for Build 2971227910

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 6 unchanged lines in 1 file lost coverage.
• Overall coverage remained the same at 39.819%

---

Files with Coverage Reduction	New Missed Lines	%
pkg/controller.v1/mpi/mpijob_controller.go	6	77.08%

Totals
Change from base Build 2889654997:	0.0%
Covered Lines:	2331
Relevant Lines:	5854

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💛 - Coveralls

[terrytangyuan]

/lgtm
/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: denkensk, terrytangyuan

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