Request improvement for faq 15.2

[Live user]

I think 15.2.2 should go before 15.1.1, since if there's no point in 
running pkg_* when the PKG_PATH is empty, which is after installing 
using the interactive method.

Furthermore, using 'export PKG_PATH=' sets a volatile variable, which in 
blank again after restarting. I think the faq may include the guideline 
to make it persistent as well.