Update functions-bindings-service-bus.md

[FinVamp1]

Updated this article to confirm that Max Concurrent calls = 16 multiplied by number of instances.

[prmerger-automator[bot]]

@FinVamp1 : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change.

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

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[v-dirichards]

@ggailey777

Can you review the proposed changes?

Important: When the changes are ready for publication, adding a #sign-off comment is the best way to signal that the PR is ready for the review team to merge.

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

[v-dirichards]

#assign: @FinVamp1

[ggailey777]

@FinVamp1 I've moved your commit + the fix we agreed on to my PR in the private repo. #please-close