Add a README.

Author: balrog-kun

README.md

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+WS2811 multiple strips library
+==============================
+
+The WS2811 RGB LED strips have extremely many potential uses.  In some
+of them, like POV displays, very high refresh rates are needed.  If all
+your LEDs are connected serially, the time required to update all of the
+pixel values or any subset of them is 30us times the total number of
+LEDs connected -- even if you don't need to update all of their colours.
+At, say, 100 LEDs that's already 3ms per refresh, which limits your
+total frame rate to 300 Hz and on an Arduino if you add all other
+overheads you may end up with even lower rates.
+
+To improve on this a little, you can connect various strips in parallel
+instead of serially, i.e. with their data lines connected to different
+Atmega GPIO pins.  The routines in this version of WS2811.h allow
+outputting the pixel data to up to 4 strips at the same time, if
+connected to GPIOs on the same Atmega port (e.g. PC0, PC1) of 2 strips
+if connected to different ports (e.g. PC2 and PB4).
+
+For example 4 strips of 25 LEDs connected to PC0 - PC3 (A0 to A3 in
+Arduino naming) can be updated in about 750us.  Not an order of
+magnitude jump but enough to make some projects practical.
+
+Further improvement
+===================
+
+With some further assumptions you can probably drive up to at least 16
+different LED strips from an Arduino, this library doesn't have any
+support for that.  It would require some preprocessing of the pixel
+data before outputting it to the AVR digital pins, so if you're
+animating something that may not be viable, but if you've got static
+data it might work.  This also requires a good amount of memory, so
+your strips probably can't be too long if you're on an Atmega328P.
+Someone has already implemented that and explains the details here
+with the 8 LED strips case:
+http://rurandom.org/justintime/index.php?title=Driving_the_WS2811_at_800_kHz_with_an_8_MHz_AVR
+
+Installation
+============
+
+Like with every Arduino library, put the files in a "libraries"
+directory in one of the various standard paths, and restart the
+Arduino IDE.  The name of the subdirectory inside "libraries" needs to
+be WS2811.  For example, clone this repository, cd inside, and do
+ln -s `pwd` ~/Arduino/libraries/WS2811