The example versioned notifications don't have any indication of
which release they are available in, and since people can link to
the 'latest' docs, like in I51d0deffc4f42ff2722a8d21aa6b8c8008c62723,
it's important to note that the samples in the latest docs might not
be in the version of nova one is actually using, e.g. ocata or pike.
So this adds a note that people should be aware of that before
relying on some versioned notification.
Change-Id: I2f7db424f0938667895b51f45ea60862a32e22c1
94ca0b9023