Update monitor-virtual-machine-alerts.md

[azarboon]

The following facts haven't been mentioned anywhere in the doc, so I've added them

"an alert rule is limited to one activity log signal. So for every condition, one alert rule must be created e.g. "starts or stops the virtual machine" requires two alert rules. However, to be alerted when VM is restarted, only one alert rule is needed. "

[prmerger-automator[bot]]

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[Court72]

@bwren

Can you review the proposed changes?

When the changes are ready for publication, add a #sign-off comment to signal that the PR is ready for the review team to merge.

#label:"aq-pr-triaged" @MicrosoftDocs/public-repo-pr-review-team

[bwren]

#sign-off

[learn-build-service-prod[bot]]

Learn Build status updates of commit bb8d7dc:

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For more details, please refer to the build report.

For any questions, please:

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