Added Cocoa example

xcode/example/readme.txt

@@ -0,0 +1,33 @@
+SFML IN COCOA APPLICATION
+=========================
+
+This is a small example of the integration of SFML in a Cocoa application.
+
+System Requirements
+-------------------
+
+In order to run this example project you need :
+ * SFML 2 compiled as shared libs (dylib) 
+   and installed into /usr/local;
+ * Xcode 4 (thus you will need Mac OS X 10.6 or greater).
+
+Features
+--------
+
+ * This example shows how basic UI elements can interact with SFML 
+   render areas such as sf::RenderWindow (you can use sf::Window and 
+   OpenGL code too, of course).
+ * It also provides tools for converting NSString to and from 
+   std::[w]string in an Objective-C Category of NSString.
+
+Special Considerations
+----------------------
+
+While mixing SFML into a Cocoa application you have to deal with mixing
+C++ and Objective-C. In order to proceed you should use .mm extension for
+Objective-C++ files.
+
+Be aware of the limitations of Objective-C++. Please refer to the official
+documentation provided by Apple for more information.
+
+You can also work around these limitations by using CSFML.