Summarize the ACRN contributing guidelines (fully documented in a
separate document) and add to the top level of our project repo (as
expected by GitHub and our Technical Steering Committee)
Also, tweak the mailing list reference to recommend acrn-users instead
of acrn-dev
Signed-off-by: David B. Kinder <david.b.kinder@intel.com>
David B. Kinder