Add minimal README (#65)

Author: karimnaaji

README.md

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+Tangram Unity
+=============
+
+
+![screenshot](tangram-unity.png)
+
+Tools for using Mapzen vector tiles in the Unity engine. The repository contains the assets and main plugin to design and generate a map region to be used in your Unity scene.
+
+Quickstart
+-----------
+
+1. Create a [Mapzen API Key](https://mapzen.com/developers/sign_up)
+2. Open the Unity plugin project
+4. Drag and drop `Assets/Mapzen.prefab` in a Unity scene
+4. Create a new _style_ to selectively generate and filter data for your map region: Assets > Create > Mapzen > Style
+5. Start authoring the style by adding filters to select map layers and associate them with materials
+6. Select the game object `Mapzen`
+	- Add your API key created in 1.
+	- Reference the newly created style asset in `Feature styling`
+	- Give a a region name
+	- Hit the `Download` button
+
+Roadmap
+-------
+
+- Terrain support
+- Tile streaming 
+- Map data access from game objects
+