Fix setup instructions to work on a clean Ubuntu installation (threat…

…9#564)

README.md

@@ -53,6 +53,7 @@ sudo add-apt-repository universe
 sudo apt-get install git python3-pip
 git clone https://www.github.com/threat9/routersploit
 cd routersploit
+python3 -m pip install setuptools
 python3 -m pip install -r requirements.txt
 python3 rsf.py
 ```