Add notes about 'arc' and 'noarc' branches

README.markdown

@@ -63,6 +63,13 @@ For example, if the subject exposes a numeric property, then that value will be
                withValueTransform:^(id value) { return [value stringValue]; }];
 
 
+## ARC Support
+
+The `master` branch does not support ARC. If you use the `KJBindingManager` class in an ARC project, you will need to add the `-fno-objc-arc` compiler option for `KJBindingManager.m`.
+
+An experimental branch, `arc`, has the code from the `master` branch converted to ARC. It has not been extensively tested, but the ARC version will eventually be moved into `master`, and the `noarc` branch will contain the old code.
+
+
 
 ## Future Directions