Update GET_STARTED.md with Ubuntu installation steps

[pranitsh]

Added instructions for installing libfuse2 on Ubuntu.

$ ./Qopy-0.3.3.AppImage
dlopen(): error loading libfuse.so.2

AppImages require FUSE to run. 
You might still be able to extract the contents of this AppImage 
if you run it with the --appimage-extract option. 
See https://github.com/AppImage/AppImageKit/wiki/FUSE 
for more information

libfuse2 is required and can be installed via the below:

sudo apt install libfuse2