Add debian/ubuntu command to get dependencies

[kaixoo]

I spent a lot of time figuring out the dependencies. I added a command in the building guide for debian / ubuntu that lets you get them all.

I also added a warning on how to get Qt officially and a way to get it without registering a Qt Account.

In the future we need to work on the Windows documentation for beginners and improve the current one for linux/mac

• Clear instructions on how to get Qt
• A script to get dependencies on all platforms

[kaixoo]

Perhaps the upper note about compiling Qt isn't necessary? (Yet).

Could build friction (after hours of googling) by installing:

sudo apt install qt5base qtdeclarative5-dev qml-module-qtquick-controls qtmultimedia5-dev

[kaixoo]

Things people have gotten stuck at in Discord:

• Downloading Qt Commercial instead of Qt Open Source.
• Knowing that friction sdk exists and how to use it.
• Missing Qt >5.15.3 from Qt installer (but qt6 is available. outdated installer?).
• Convenience script that automatically downloads dependencies for windows.
• Impossible to install older versions of ffmpeg-devel in fedora.