README: add install from package section

Signed-off-by: Dongsheng Yang <[email protected]>

README.md

@@ -36,10 +36,16 @@ Who should not use UBBD?
 	   $ cd ubbd
 	   $ ./build_and_install.sh
 
-**install from package**
+**install from script**
 
 	bash -c "$(wget https://raw.githubusercontent.com/DataTravelGuide/ubbd/master/install-ubbd.sh -O -)"
 
+**install from package**
+
+	$ sudo add-apt-repository ppa:datatravelguide/ppa
+	$ sudo apt update
+	$ sudo apt install ubbd ubbd-kernel -y
+
 # 5. performance
 
 5.1）We can get **2 million** iops with null type ubbd device.