NormalTangentMirrorTest README contains erroneous instructions

[warrenm]

The README for the NormalTangentMirrorTest sample asset contains the following text:

"Note that this model (NormalTangentTest) does not supply tangent vectors, and specifically tests a rendering engine's ability to generate the tangent vectors at runtime. To test supplied tangent vectors, see NormalTangentMirrorTest."

It appears that this text was copied from the NormalTangentTest asset unmodified, but it does not apply to NormalTangentMirrorTest (which does, in fact, supply tangents). I feel the two sentences referenced above could be removed, or they could be replaced with other language pertaining to the model's contents.