openSUSE Build server instuctions update Debian/Ubuntu

[gbWilly <gbWilly@xxxxxxxxxxxxxx>]

Hello,

A few days ago, I did a little redo of the instructions on how to install gambas from openSUSE Build server for both Debian and Ubuntu. They can be seen [here](https://gambaswiki.org/wiki/doc/packages).
- Instructions are now divided for master and stable
- Each OS version has got his specific set of commands to set it all up
- I added an extra note on what to do to switch from osb master to stable if desired.

Hope this makes installing on master/stable on either Debian or Ubuntu less confusing for everyone.

gbWilly

[Gambas3 for Debian/Ubuntu](https://gitlab.com/gbWilly/gambas3-debian-repository)