Fixed ubuntu pip requirements install command (threat9#400)

README.md

@@ -52,7 +52,7 @@ python3 rsf.py
 sudo add-apt-repository universe
 sudo apt-get install git python3-pip
 git clone https://www.github.com/threat9/routersploit
-python3 -m pip install -r requirements
+python3 -m pip install -r requirements.txt
 python3 rsf.py
 ```