I had to create a wireless streaming video system at work. The stream comes from a camera connected to a raspberry Pi, and use one of those cheap, wifi adapter that use Realtek chips like the 
DIZA100 Wireless USB Wifi Adapter.  Here are the step to install its driver and get things up running:

visit this guy’s GitHub: https://github.com/abperiasamy/rtl8812AU_8821AU_linux and install the driver:

git clone https://github.com/abperiasamy/rtl8812AU_8821AU_linux.git
sudo apt install git raspberrypi-kernel-headers make gcc
cd rtl8812AU_8821AU_linux

Edit Makefile and turn on CONFIG_PLATFORM_ARM_RPI, turn off CONFIG_PLATFORM_I386_PC

CONFIG_PLATFORM_I386_PC = n
CONFIG_PLATFORM_ARM_RPI = y

make
sudo insmod 8812au.ko
sudo cp 8812au.ko /lib/modules/$(uname -r)/kernel/drivers/net/wireless
sudo depmod

To completely disable the onboard WiFi from the firmware on the Pi3, add

dtoverlay=pi3-disable-wifi

in /boot/config.txt.

git clone https://github.com/unixabg/RPI-Wireless-Hotspot.git

Navigate to folder, and execute:

sudo ./install

This should automatically set everything up and leave you ready to go

follow this guy’s instruction without cloning his repo: https://qiita.com/kangaechu/items/6ad07854f00bb902f74b

The DHCP service will likely fail to start, the solution is to let in /etc/default/udhcpd DHCPD_ENABLED to “no” and add the following network configuration to /etc/network/interfaces for br0 :

post-up /usr/sbin/udhcpd -S /etc/udhcpd.conf