Update broken Links and clean up

Updated broken links after github update as explained in [This Issue](https://github.com/omgmog/archarm-usb-hp-chromebook-11/issues/15)

Also shortened pacman command from two lines to one (in a previous commit I added the pacman command to install libgl-mesa separatly in order to be sure it wouldn't work ( see the [Related Issue](https://github.com/omgmog/archarm-usb-hp-chromebook-11/issues/12)