Updated Registration Instructions

Documents the changes made in commit
8ee282b1aa

CONTRIBUTING.md

@@ -20,9 +20,11 @@ click through the warnings to allow the certificate. If at any time you notice
 a console error about an "INSECURE RESPONSE" or "Handshake was canceled",
 repeat this step.
 
-Once that's done, in the extension's options page, you can register for
-TextSecure:
+Once that's done, you can register for TextSecure using the instructions below:
 
+**NOTE:** This is only for developers and will not be presented to users.
+
+* Navigate to chrome-extension://.../register.html
 * Select "Register" under "I'm new to TextSecure".
 * Enter a real phone number (Google Voice numbers work too) and country
   combination and choose to send an SMS. You will receive a real SMS.