Update readme

[AKArien]

A few readme changes i felt were necessary / would be welcome.

tell me what we want and what we don’t :)

[trigg]

    XDG_CONFIG_HOME
        Where user-specific configurations should be written (analogous to /etc).
        Should default to $HOME/.config.

Looks like you've accidentally doubled your .config directories :)

[AKArien]

Also should update the github’s « about », we have more than a panel :)

[AKArien]

Also, are we looking to change the standard description of what wf-shell « is » ?
As in, old readme says « various components needed to built a fully functional DE », while the recent matrix chat room says « applications designed to be used as a Shell »
Not that they mean the opposite of each other, but i think i’d be better if everything referred to it the same way :)