Update readme with information about supported versions of debian

Hey, so we currently have working packages for Ubuntu 24.04 LTS, Ubuntu 22.04 LTS (needs !208 (merged)) and Debian 12.

The problem with Debian 11 is that it does not have the qt6 packages (only in backports). So when I install the (make) deps:

pea@debian:~$ sudo apt-get install -y golang make pkg-config g++ git libqt6svg6-dev qt6-tools-dev qt6-tools-dev-tools qt6-base-dev libqt6qml6 qt6-declarative-dev dh-golang libgl-dev  qt6-5compat-dev qt6-declarative-dev-tools qt6-l10n-tools libqt6core6 libqt6gui6 libqt6qml6 libqt6widgets6 libstdc++6 libqt6svg6 qml6-module-qtquick qml6-module-qtquick-controls qml6-module-qtquick-dialogs qml6-module-qtquick-layouts qml6-module-qtqml-workerscript qml6-module-qtquick-templates qml6-module-qt-labs-settings qml6-module-qtquick-window qml6-module-qt-labs-platform qml6-module-qtcore qml6-module-qt5compat-graphicaleffects openvpn policykit-1-gnome devscripts
[sudo] password for pea: 
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
E: Unable to locate package libqt6svg6-dev
E: Unable to locate package qt6-tools-dev
E: Unable to locate package qt6-tools-dev-tools
E: Unable to locate package qt6-base-dev
E: Unable to locate package libqt6qml6
E: Unable to locate package qt6-declarative-dev
E: Unable to locate package qt6-5compat-dev
E: Unable to locate package qt6-declarative-dev-tools
E: Unable to locate package qt6-l10n-tools
E: Unable to locate package libqt6core6
E: Unable to locate package libqt6gui6
E: Unable to locate package libqt6qml6
E: Unable to locate package libqt6widgets6
E: Unable to locate package libqt6svg6
E: Unable to locate package qml6-module-qtquick
E: Unable to locate package qml6-module-qtquick-controls
E: Unable to locate package qml6-module-qtquick-dialogs
E: Unable to locate package qml6-module-qtquick-layouts
E: Unable to locate package qml6-module-qtqml-workerscript
E: Unable to locate package qml6-module-qtquick-templates
E: Unable to locate package qml6-module-qt-labs-settings
E: Unable to locate package qml6-module-qtquick-window
E: Unable to locate package qml6-module-qt-labs-platform
E: Unable to locate package qml6-module-qtcore
E: Unable to locate package qml6-module-qt5compat-graphicaleffects
pea@debian:~$ 

So for example qt6-base-dev is in bookworm but not in bullseye. It is also in bullseye-backports, but we can not expect poeple to have that? So Debian 11 is out of support I guess?

@jkito @kwadronaut