mkdir -p is better than just mkdir in the documentation

Hey,

on this page:
https://www.torproject.org/docs/debian.html.en

The command:
mkdir ~/debian-packages; cd ~/debian-packages

Would be better like this, because then it would not generate an error when the directory already exists from a previous version's build:
mkdir -p ~/debian-packages; cd ~/debian-packages

BR

Trac:
Username: daffyduck