Please fix Installation instruction for Debian in README.md

[Anthony Fok]

Hi Eduards,

In the current README.md, the installation instruction for Debian currently reads:

  #### Debian
  Until recently there was no easy way of using Timekpr-nExT in Debian,
  but thanks to Sim (smntov) and Anthony Fok (foka), Timekpr-nExT is /
  will be available in Debian as native installation via Software Center.

The preferred method of installing timekpr-next on Debian is just like on Ubuntu:

    sudo apt-get update
    sudo apt-get install timekpr-next

No, never (or almost never) in Software Center. AFAIK, The "Ubuntu Software Center" https://en.wikipedia.org/wiki/Ubuntu_Software_Center never quite caught on in Debian... or did it exist in Debian at all? "Ubuntu Software Center" replacement "GNOME Software" https://en.wikipedia.org/wiki/GNOME_Software well, it is not my go-to for installing software on Debian either.

The reason I mentioned Software Center / GNOME Software and AppStream in the past was simply to report Lintian warnings and errors. I was thinking that perhaps with correct AppStream metadata Timekpr-nExT would get properly listed in AppStream and thus appear properly on GNOME Software, thus increasing Timekpr-nExT visibility.

But then, it seems that GNOME Software could be flaky... right now on my machine, GNOME Software is malfunctioning and fails to show any package... but killing the gnome-software process and restarting fixes it. Hey, it works now!

(You can probably tell how unfamiliar I am with GNOME Software for Debian package installation...)

Anyhow, I think apt-get is still the most surefire way to install timekpr-nExT on Debian.

That said, please feel free to keep the reference to "GNOME Software" and/or KDE's equivalent "Plasma Discover", both of which are able to see Timekpr-nExT in the Debian archive and to act as front-end for APT to install Timekpr-nExT...

Many thanks!

Anthony