Release dist for Ubuntu 20.04 in ppa

[Stuart Mitchell]

Currently it is not there :-(

and gives the following cryptic error

E: The repository 'http://ppa.launchpad.net/mfikes/planck/ubuntu focal Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.```

[Sean Corfield]

As a data point, I was able to planck installed just now with the PPA instructions (from my history):

  225  sudo add-apt-repository ppa:mfikes/planck
  226  sudo apt update
  227  sudo apt-get install planck

Planck worked as expected immediately after this.

[Mike Fikes]

Yes, I added Focal in July.