Update readme for adding a note about pigz.
Update readme for adding a note about pigz.

invenfantasy/software-factory,invenfantasy/software-factory,invenfantasy/software-factory,enovance/software-factory,enovance/software-factory,enovance/software-factory,invenfantasy/software-factory,enovance/software-factory,invenfantasy/software-factory,enovance/software-factory