doc: update focal

Author: fcwu

README.md

@@ -23,10 +23,12 @@ Browse http://127.0.0.1:6080/
 
 Choose your favorite Ubuntu version with [tags](https://hub.docker.com/r/dorowu/ubuntu-desktop-lxde-vnc/tags/)
 
-- bionic: Ubuntu 18.04 (latest)
+- focal: Ubuntu 20.04 (latest)
+- focal-lxqt: Ubuntu 20.04 LXQt
+- bionic: Ubuntu 18.04
 - bionic-lxqt: Ubuntu 18.04 LXQt
-- xenial: Ubuntu 16.04
-- trusty: Ubuntu 14.04
+- xenial: Ubuntu 16.04 (deprecated)
+- trusty: Ubuntu 14.04 (deprecated)
 
 VNC Viewer
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