Add readme

Author: marijnvdwerf

README.md

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+Palette for PHP
+===============
+
+![Logo](docs/artwork.png)
+
+**Palette** is a port of the Android library of the same name, for extracting a colour palette from an image. The
+results can then be used for tinting the interface to match the image.
+
+Usage
+-----
+Palette makes use of the [Intervention image library](https://github.com/Intervention/image) to load images, and supports
+both the Imagick and GD drivers. The performance of the Imagick driver is slightly better, but the difference is fairly small.
+
+```php
+$manager = new ImageManager(array('driver' => 'imagick'));
+$image = $manager->make('path/to/image.png');
+
+$palette = Palette::generate($image);
+echo $palette->getVibrantSwatch()->getColor();
+``
+
+Contrast
+--------
+You can get the contrast of a colour on a non-translucent background by calling
+`AbstractColor::calculateContrast($background, $foreground)`. Information on the recommended contrast ratio can be found
+at [the W3C recommendation](http://www.w3.org/TR/WCAG/#visual-audio-contrast-contrast).
+
+```php
+$white = new RGBColor(1, 1, 1);
+$black = new RGBColor(0, 0, 0);
+$background = $palette->getVibrantSwatch()->getColor();
+
+echo '<div style="background: ' . $background . '">';
+if(AbstractColor::calculateContrast($background, $white) >= 3) {
+    echo '<h1 style="color: white;">Palette</h1>';
+} else {
+    echo '<h1 style="color: black;">Palette</h1>';
+}
+echo '</div>';
+```