Add known issue about confusing log.
Add known issue about confusing log.

Bug: https://github.com/google/perfetto/issues/90
Change-Id: I994bd7181f80f98ba4aed8bc6269e2dc54eb277d
google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto