Update configure-authentication-customize-sign-in-out.md: domain hint clarification

[fowl2]

Don't suggest that it "limits" anything, as it's just a hint.

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[Court72]

@cephalin

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"

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[cephalin]

sign-off

[Court72]

Due to the upcoming Build conference, all merging and publishing is on hold until the morning of 5/21.

This PR is ready for merge on 5/21.

label: "event-triaged-to-10AM"

label: "missed-content-complete"