slightly imprecise installation instructions


under "All Ubuntu versions (old and new) can get the newest packages from Debian Sid", it says:

Download arduino and arduino-core .debs into a clean directory from: (Uno/Mega2560 owners also need

Indeed, everybody also needs librxtx-java, as it is a dependency of the arduino package, which will refuse to install if you don't have the librxtx-java package installed