[ReleasePR preview/deviceupdate/mgmt/2020-03-01-preview/deviceupdate] update readme#15607

Closed

openapi-sdkautomation[bot] wants to merge 1 commit intoAzure:mainfrom AzureSDKAutomation:sdkAuto/preview_deviceupdate/mgmt/2020-03-01-preview/deviceupdate

+1,666-74