PPA update for Ubuntu 18.04

Good news is that the soapysdr and friends packages are in the official ubuntu package repositories: https://packages.ubuntu.com/search?keywords=soapysdr&searchon=names&suite=bionic&section=all

One item of note is that apt-get install soapysdr becomes apt-get install soapysdr-tools. It looks like the upstream ubuntu/debian packaging renamed this, I will have to look at backporting it to the PPA and renaming the instructions to match.

I’m aware the pothosware ppa is not updated yet. I just tagged a release yesterday. I like to update to the latest release at the same time so I dont have to do it twice. It should be up soon, there is an open issue which I will close when ready: https://github.com/pothosware/PothosCore/issues/160