Update the build instructions based on recent experience.
Update the build instructions based on recent experience.

The non-mac v2.3rc2 builds were built on clean Amazon virtual machines and so I had to follow the build instructions to get the machines set up.  Plus now we are building for Python 3 as well as Python 2.  I have tweaked the build instructions based on that experience.

adorton-adobe/user-sync.py,adobe-apiplatform/user-sync.py,adobe-apiplatform/user-sync.py,adorton-adobe/user-sync.py