Steps to use usb wifi Dongle on Pynq -

Method 1 - Using Python3.6

from pynq import Overlay
from pynq.lib.usb_wifi import Usb_Wifi
Usb_Wifi().connect("ssid_name", "passphrase")

Method 2 - Using bash

Step 1:
wpa_passphrase "ssid_name" "passphrase"
This command should generate output like :
network={
        ssid="ssid_name"
        #psk="passphrase"
        psk=2b1d17284c5410ee5eaae7151290e9744af2182b0eb8af20dd4ebb415928f726
}

Step 2: Plug in the usb wifi and find interface name using:
ip a  | grep -iE '^[0-4]: w.*'

Suppose you get interface name as 'wlx00f000356eae'

Step 3:
sudo vim /etc/network/interfaces.d/wlx00f000356eae

Edit the file to look like :
iface wlx00f000356eae inet dhcp
 wpa-ssid ssid_name
 wpa-psk 2b1d17284c5410ee5eaae7151290e9744af2182b0eb8af20dd4ebb415928f726

Step 4:
sudo ifup wlx00f000356eae