update solus flatpak guide in github

I was asked questions for which I can't answer, probably the help of @DataDrake and @JoshStrobl , because this is due to architectural features.

(if you installed repo flatpak w/o sudo error occurs: Creating repo: mkdirat:access denied)

In my case it shows a password prompt when running it without sudo and then works fine after entering it (using Budgie)

Yea it doesn't need sudo, it will prompt accordingly.

JoshStrobl mmmh just checked with a fresh budgie install and get the same error as with plasma

On Solus Plasma it doesn't prompt for a password if you run it without sudo. Instead it fails with the error message posted above.

Just tested this on a fresh install of 4.3