Added a README.

README.md

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+Water Demo
+==========
+
+This is a port of Evan Wallace's [Water Demo](http://madebyevan.com/webgl-water/) from WebGL to Unity.
+
+Motivation
+----------
+
+I ported this as an exercise to investigate different caustics implementations.  Having surveyed research papers on real-time caustics, I believe Evan's work supercedes many published algorithms in terms of simplicity and performance and is suitable for publication.
+
+Requirements
+------------
+
+* Unity 2018.2.17f1
+
+Implementation Notes
+--------------------
+
+This is a pretty faithful reproduction of Evan's demo.  As such there are a number of cases where it deviates from Unity's conventions.
+
+For instance, the shader that renders the sphere has variable `sphereCenter`, so the sphere rendering object is expected to located at the origin and if you change that, it probably will not look right.
+
+The light direction is provided to shaders as a vector.  It doesn't use Unity's lighting at all.
+
+The models' vertices do not have UV coordinates.  For instance the cube's minimum and maximum model position are (-1, -1, -1) and (1, 1, 1), so any point on its surface is often just mapped directly to a UV coordinate [0, 1]^2 by transforming the point p by `p * 0.5 + 0.5`.  This works fine for the purposes of the demo, but one would probably want to switch to UV coordinates in the future.
+
+A lot of this is smoke and mirrors. The cube knows where the sphere is, so it renders its shadow. Great for a tech demo, but if you want to allow for multiple spheres or other objects, this will need to be reformulated significantly.
+
+Bugs
+----
+
+See the `todo.org` file.
+
+License
+-------
+
+This project is released under the MIT license.