Update Readme: target directory of udev files

[manum45]

I think the target directory for the udev files should be in /etc/udev/rules.d.

There is some discussion online about which is the right place to add user rules, and I could find no consensus, but /etc/udev/rules.d seems to be preferred over /usr/lib/udev/rules.d.

https://unix.stackexchange.com/questions/333697/etc-udev-rules-d-vs-lib-udev-rules-d-which-to-use-and-why
https://unix.stackexchange.com/questions/732279/does-the-location-of-package-installed-udev-rules-differ-across-linux-distributi

Also oversteer itself tries to copy the rules files to /etc/udev/rules.d.

oversteer/oversteer/application.py

Line 18 in 74c7484

self.target_dir = '/etc/udev/rules.d/'

So I think this is the directory that should be mentioned in the readme.

As a sidenote, on an Fedora Atomic Desktop I'm not even able to write to the /usr/lib/udev.