title: how to use tensorflow-lite nnapi on android 7 & 8
body: <p>NNAPI is available on android 8.1.
  But I want to use the NNAPI on android 7&amp;8(arm64). 
  the NNAPI is used by tensorflow-lite.</p>
  
  <p>Where can I download libneuralnetworks.so?</p>