update documentation

Author: akhenakh

README.md

@@ -16,8 +16,9 @@ It provides:
 - A guarantee that main thread will never be blocked
 - Performances!
 - Use GCD and ARC
+- Arm64 support
 
-NOTE: The version 3.0 of SDWebImage isn't fully backward compatible with 2.0 and requires iOS 5.0
+NOTE: The version 3.0 of SDWebImage isn't fully backward compatible with 2.0 and requires iOS 5.1.1
 minimum deployement version. If you need iOS < 5.0 support, please use the last [2.0 version](https://github.com/rs/SDWebImage/tree/2.0-compat).
 
 [How is SDWebImage better than X?](https://github.com/rs/SDWebImage/wiki/How-is-SDWebImage-better-than-X%3F)