documentation for partition size distribution from extract-partitions.py

[chuckpr]

extract-partitions.py doesn't specify what the columns are in the .dist output file. Not sure where to add this info. Maybe in the epilog? Could also be included in what's printed to stdout (and/or the script's docstring although that won't be printed when the script is called).

[mr-c]

Thank you @chuckpr for catching this.

That should go in the epilog, yes.

[chuckpr]

This was addressed in #516.