Updated README to highlight ARC compatibility.

Author: michaelkamprath

README

@@ -1,3 +1,5 @@
 iPhoneMK is a loose collection of Objective-C classes for the iPhone SDK that I have put together over time which I feel might be of general utility to people. The classes are released under the Apache 2.0 license.
 
-If you find any of these classes useful, I'd love to hear about it. If you have improvements for any of them, feel free to commit your changes, however, I ask that you try not to change existing interface.
+If you find any of these classes useful, I'd love to hear about it. If you have improvements for any of them, feel free to commit your changes, however, I ask that you try not to change existing interface.
+
+NOTE - iPhoneMK is not ARC-enabled code. You will need to use the -fno-objc-arc compiler flag on iPhoneMK source files in ARC-enabled projects.