Fix #1680

README.md

@@ -101,6 +101,7 @@ sudo apt -t stretch-backports install shadowsocks-libev
 For **Ubuntu 14.04 and 16.04** users, please install from PPA:
 
 ```bash
+sudo apt-get install software-properties-common -y
 sudo add-apt-repository ppa:max-c-lv/shadowsocks-libev
 sudo apt-get update
 sudo apt install shadowsocks-libev