Add missing icons to .local/share/icons for Linux

[rehhouari]

SGDBoop doesn't add any icon to .local/share/icons/hicolor meaning even if I apply an icon it would still show the steam default one in the desktop or application menus. Regardless if I apply the sgd icon before I install the game or after.**

I think this feature would be be so helpful and thank you for this app!

System: arch, steam runtime (not flatpak), sdgboop: flatpak