Add README to NeuralNetworks HAL

Adds README explaining where to find the NeuralNetworks sample driver.

Test: N/A

Merged-In: Ifbbbbb3801176da27fb03bbed0b0d739031a195b
Change-Id: Ifbbbbb3801176da27fb03bbed0b0d739031a195b
(cherry picked from commit 3530f9ef0dbda90309ddfc626bc3d363e32dcb99)
1 file changed