blink1: Update README.md with udev instructions for Linux.

Chrome on Linux needs a new udev rule for this device in order for an
unprivileged user to open it.
Suggest restricting HID access to the plugdev group.

Change the suggested udev rule to only give users in the plugdev group
access to the blink(1)'s hidraw device node. This is more secure.
blink1: Add more links to README.md and reorder sections.

Add an internal link to the udev rules file and a link to the Chrome
documentation for adding udev rules for USB devices (though I suggest
slightly different rules for HID devices).

Reorder the "Running this app on Linux" section above "Screenshot".
Merge pull request #286 from reillyeon/blink1

blink1: Update README.md with udev instructions for Linux.