Update README.md

Author: jackykongfz

README.md

@@ -5,6 +5,10 @@ Paper is available on Arxiv: https://arxiv.org/abs/2211.10716
 
 The video is available on youtube: https://youtu.be/hiRtcq-5lN0
 
+## Update
+
+Ubuntu 20.04 is also supported in ubuntu20 branch.
+
 ## Prerequisited
 
 ### Ubuntu and ROS
@@ -47,4 +51,4 @@ You can change the parameter in launch files to change the map and LiDAR to be s
 Thanks for [FUEL](https://github.com/HKUST-Aerial-Robotics/FUEL.git)
 
 ## Future
-More realistic maps and functions are going to be released soon.
+More realistic maps and functions are going to be released soon.