add brief explanation about PDK repository

Change-Id: Ib45aadfd4aa38b4a2162249c04a2e43b0a367f6a
1 file changed
tree: e52647a12eacfa2a2f3b2e3cb5a31b7004496638
  1. apps/
  2. build/
  3. .gitignore
  4. README