Update mx-linux/mx-21-docker.sh

mx-linux/mx-21-docker.sh

@@ -6,6 +6,7 @@ sudo apt install -y ca-certificates gnupg-agent apt-transport-https curl softwar
 curl -fsSL https://download.docker.com/linux/debian/gpg | sudo apt-key add -
 sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/debian $(lsb_release -cs) stable"
 sudo apt update
+sudo apt install -y cgroupfs-mount
 sudo apt install -y docker-ce docker-ce-cli containerd.io
 sudo service docker start
 sudo update-rc.d docker enable