add pip to netstat to code example

Example 1: netstat install

# apt install net-tools     [On Debian/Ubuntu]

Example 2: install netstat linux centos 7

# yum install net-tools     [On CentOS/RHEL]
# apt install net-tools     [On Debian/Ubuntu]
# zypper install net-tools  [On OpenSuse]
# pacman -S netstat-nat     [On Arch Linux]