Installation guide fix

[florianspy]

The guide give on below of Installation and Usage needs to minor fixes
after the cd ds4drv
mkdir ~/.local/lib/python2.7/site-packages
or else you get errors that this path does not exist
and before the line
sudo cp 50-ds4drv.rules /etc/udev/rules.d/
the command
cd udev

[naoki-mizuno]

Thanks for reporting!