Missing instructions for Ubuntu installation / Ondrej Sury PPA

[Murilo]

I accessed the project website because I was expecting to find the PPA maintened by Ondrej Sury with the latest PHP versions for Ubuntu and Debian based distros. Unfortunately, I had to search the web a little more.

Since I coudln't find that, neither a related issue, I am creating the issue and I'll be trying to submit a PR to fix that.