improve documentation for udev rule files on Linux (libusb#276)

- use TAG+="uaccess" instead of overly broad MODE="0666" by default example
        as advised by Debian:
        https://lists.debian.org/debian-devel-announce/2016/11/msg00008.html
        Adding the uaccess tag to udev rules
        ------------------------------------
Packages containing udev rules that use GROUP="plugdev" should also add
 TAG+="uaccess" so that all users that are physically present can access
 the relevant devices, instead of just users in the plugdev group
 (GROUP="plugdev"). Some packages use MODE="666" to allow all users
 (including remote users) to access devices. For almost all devices it is
 probably more appropriate to switch from MODE="666" to GROUP="plugdev",
 MODE="660", TAG+="uaccess" so that remote users cannot access local
 devices. Check the wiki page for USB gadgets[13] for more hints.
 There is a lintian warning in progress[14] for these issues.
  -- Paul Wise & Petter Reinholdtsen
 [] https://wiki.debian.org/USB/GadgetSetup
 [] https://bugs.debian.org/841670

- remove documentation for Linux <2.6.24

Author: Be-ing

README.md

@@ -50,6 +50,11 @@ built by default. It is up to the application linking to hidapi to choose
 the backend at link time by linking to either `libhidapi-libusb` or
 `libhidapi-hidraw`.
 
+Note that you will need to install a udev rule file with your application
+for unprivileged users to be able to access HID devices with hidapi. Refer
+to the [69-hid-udev.rules](udev/69-hid-udev.rules) file in the `udev` directory
+for an example.
+
 __Linux/hidraw__ (`linux/hid.c`):
 
 This back-end uses the hidraw interface in the Linux kernel, and supports

udev/69-hid.rules

@@ -0,0 +1,33 @@
+# This is a sample udev file for HIDAPI devices which lets unprivileged
+# users who are physically present at the system (not remote users) access
+# HID devices.
+
+# If you are using the libusb implementation of hidapi (libusb/hid.c), then
+# use something like the following line, substituting the VID and PID with
+# those of your device.
+
+# HIDAPI/libusb
+SUBSYSTEM=="usb", ATTRS{idVendor}=="04d8", ATTRS{idProduct}=="003f", TAG+="uaccess"
+
+# If you are using the hidraw implementation (linux/hid.c), then do something
+# like the following, substituting the VID and PID with your device.
+
+# HIDAPI/hidraw
+KERNEL=="hidraw*", ATTRS{idVendor}=="04d8", ATTRS{idProduct}=="003f", TAG+="uaccess"
+
+# Once done, optionally rename this file for your application, and drop it into
+# /etc/udev/rules.d. Note that these rules must have priorty before 70-uaccess.rules
+# for example, name the file /etc/udev/rules.d/69-my-application-hid.rules.
+# Then, replug your device or run:
+# sudo udevadm control --reload-rules && sudo udevadm trigger
+
+# Note that the hexadecimal values for VID and PID are case sensitive and
+# must be lower case.
+
+# TAG+="uaccess" only gives permission to physically present users, which
+# is appropriate in most scenarios. If you require remote access to the
+# device, add
+# GROUP="plugdev", MODE="660"
+# to the end of the udev rule lines, add your user to the plugdev group with:
+# usermod -aG plugdev USERNAME
+# then log out and log back in (or restart the system).