Add helper script for simplified pbulk setup.

The script serves several purposes. Chief of them:
1. Fast track for those who just want to build their 1000 packages
and do not want to bother with optimizations.
2. Fast track for those who want to understand how pbulk is supposed
to be set up.

Because it serves as a documentation (providing working setup at the same time),
a lot of features are intentionally left out.

(asau)