2.16 release notes: Mention the system property that must be set for tracing
2.16 release notes: Mention the system property that must be set for tracing

Change-Id: Id6f0ef6d7bd0445f1c07480a860cab6b871bbd91
Signed-off-by: Edwin Kempin <d43fb6c98c97e553b671ed9a9318100f1de386e7@google.com>

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