README: add helperbit

Author: dcousens

README.md

@@ -136,6 +136,7 @@ If you have a use case that you feel could be listed here, please [ask for it](h
 - [Dogechain Wallet](https://dogechain.info)
 - [EI8HT Wallet](http://ei8.ht/)
 - [GreenAddress](https://greenaddress.it)
+- [Helperbit](https://helperbit.com)
 - [Melis Wallet](https://melis.io)
 - [Robocoin](https://wallet.robocoin.com)
 - [Skyhook ATM](http://projectskyhook.com)