Add unmaintained note

Please merge this, @sebsauvage.

Author: rugk

README.md

@@ -1,3 +1,13 @@
+## This repo is unmaintained and outdated! Do not use this code anymore! :warning: 
+
+**If you still use this old code switch to the new maintained repo:**  
+**:arrow_forward: https://github.com/elrido/ZeroBin**
+
+You will get more features and up-to-date code. 
+
+====
+----
+
 ZeroBin 0.19 Alpha
 
 ==== THIS IS ALPHA SOFTWARE - USE AT YOUR OWN RISKS ====