[cocos2d-objc] Updated README to explain how to handle ARC.

spine-cocos2d-objc/README.md

@@ -22,6 +22,7 @@ spine-cocos2d-objc does not yet support loading the binary format.
 2. Download the Spine Runtimes source using git (`git clone https://github.com/esotericsoftware/spine-runtimes`) or download it [as a zip](https://github.com/EsotericSoftware/spine-runtimes/archive/3.6.zip)
 3. Add the sources from `spine-c/spine-c/src/spine` and `spine-cocos2d-objc/src/spine` to your project
 4. Add the folders `spine-c/spine-c/include` and `spine-cocos2d-objc/src` to your header search path. Note that includes are specified as `#inclue <spine/file.h>`, so the `spine` directory cannot be omitted when copying the source files.
+5. If your project uses ARC, you have to exclude the `.m` files in `spine-cocos2d-objc/src` from ARC. See https://stackoverflow.com/questions/6646052/how-can-i-disable-arc-for-a-single-file-in-a-project for more information.
 
 See the [Spine Runtimes documentation](http://esotericsoftware.com/spine-documentation#runtimesTitle) on how to use the APIs or check out the Spine cocos2d-objc example.