Announce availability of updated Sandstorm SPK

minor edit

README.md

@@ -21,6 +21,8 @@ Host your own Rocket.Chat server in four seconds flat:
 
 [![Rocket.Chat on Sandstorm.io](https://raw.githubusercontent.com/Sing-Li/bbug/master/images/sandstorm.jpg)](https://apps.sandstorm.io/app/vfnwptfn02ty21w715snyyczw0nqxkv3jvawcah10c6z7hj1hnu0)
 
+_*Grab*_ the latest [Sandstorm SPK](https://s3.amazonaws.com/rocketchatbuild/rocket.chat.latest.spk) for testing on your own server.
+
 Also available as FirefoxOS app:
 
 [![Firefox OS app now available](https://raw.githubusercontent.com/Sing-Li/bbug/master/images/firefoxos.png)](https://github.com/RocketChat/Rocket.Chat/wiki/Native-Firefox-OS-app-%28hosted-webapp%29)