Add notice about 3.0 beta

README.md

@@ -1,6 +1,8 @@
 Web Image
 =========
 
+> **Psst! [SDWebImage 3.0 beta](https://github.com/rs/SDWebImage/tree/3.0-beta) is out!**
+
 This library provides a category for UIImageVIew with support for remote images coming from the web.
 
 It provides:
@@ -12,6 +14,7 @@ It provides:
 - A guarantee that bogus URLs won't be retried again and again
 - Performances!
 
+
 Motivation
 ----------