IVGCVSW-3138 Update README.md in android-nn-driver
IVGCVSW-3138 Update README.md in android-nn-driver

 * Updated the information on the supported Android versions.

Signed-off-by: Mike Kelly <e10d499d2073d26b149e114dc8420d8f96d919f9@arm.com>
Change-Id: I1f674baec7633906e15cf148472f7da1960ba2a2

ARM-software/android-nn-driver,ARM-software/android-nn-driver