add the example of MPIJob

[hackerboy01]

#1502 add the example of MPIJob in the kubeflow/training-operator.

[coveralls]

Pull Request Test Coverage Report for Build 1572177921

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 16 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.3%) to 27.491%

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Files with Coverage Reduction	New Missed Lines	%
pkg/controller.v1/mpi/mpijob_controller.go	7	75.02%
pkg/controller.v1/pytorch/pytorchjob_controller.go	9	61.65%

Totals
Change from base Build 1545960757:	-0.3%
Covered Lines:	1680
Relevant Lines:	6111

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💛 - Coveralls

[terrytangyuan]

Thanks!

/lgtm
/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hackerboy01, terrytangyuan

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