Update README

Author: pvigier

README.md

@@ -6,23 +6,46 @@ I wrote an [article](https://pvigier.github.io/2018/06/13/perlin-noise-numpy.htm
 
 A fast and simple perlin noise generator using numpy.
 
-The function `generate_perlin_noise_2d` generates the classical perlin noise. Its parameters are:
+### 2D noise
 
-* `shape`: shape of the generated array (tuple of ints)
-* `res`: number of periods of noise to generate along each axis (tuple of ints)
+The function `generate_perlin_noise_2d` generates a 2D texture of perlin noise. Its parameters are:
+
+* `shape`: shape of the generated array (tuple of 2 ints)
+* `res`: number of periods of noise to generate along each axis (tuple of 2 ints)
+
+Note: `shape` must be a multiple of `res`
+
+The function `generate_fractal_noise_2d` combines several octaves of 2D perlin noise to make 2D fractal noise. Its parameters are:
+
+* `shape`: shape of the generated array (tuple of 2 ints)
+* `res`: number of periods of noise to generate along each axis (tuple of 2 ints)
+* `octaves`: number of octaves in the noise (int)
+* `persistence`: scaling factor between two octaves (float)
+
+Note: `shape` must be a multiple of `octaves*res`
+
+
+### 3D noise
+
+The function `generate_perlin_noise_3d` generates a 3D texture of perlin noise. Its parameters are:
+
+* `shape`: shape of the generated array (tuple of 3 ints)
+* `res`: number of periods of noise to generate along each axis (tuple of 3 ints)
 
 Note: `shape` must be a multiple of `res`
 
-Moreover the function `generate_fractal_noise_2d` combines several octaves of perlin noise to make fractal noise. Its parameters are:
+The function `generate_fractal_noise_2d` combines several octaves of 3D perlin noise to make 3D fractal noise. Its parameters are:
 
-* `shape`: shape of the generated array (tuple of ints)
-* `res`: number of periods of noise to generate along each axis (tuple of ints)
+* `shape`: shape of the generated array (tuple of 3 ints)
+* `res`: number of periods of noise to generate along each axis (tuple of 3 ints)
 * `octaves`: number of octaves in the noise (int)
 * `persistence`: scaling factor between two octaves (float)
 
 Note: `shape` must be a multiple of `octaves*res`
 
 ## Gallery
 
-![Perlin noise](https://github.com/pvigier/perlin-numpy/raw/master/examples/perlin2d.png)
-![Fractal noise](https://github.com/pvigier/perlin-numpy/raw/master/examples/fractal2d.png)
+![2D Perlin noise](https://github.com/pvigier/perlin-numpy/raw/master/examples/perlin2d.png)
+![2D fractal noise](https://github.com/pvigier/perlin-numpy/raw/master/examples/fractal2d.png)
+![3D Perlin noise](https://github.com/pvigier/perlin-numpy/raw/master/examples/perlin3d.gif)
+![3D fractal noise](https://github.com/pvigier/perlin-numpy/raw/master/examples/fractal3d.gif)