remove helptext to input "Custom URL" in the user settings when not using this feature

Issue Summary

thanks for this great module. One minor thing confuses my users: "In the Custom URL on Ping.fm, enter the following: "http://..."
Since I don't want users to post from remote and don't have the ping.fm node module enabled, this is not needed. Also the "...to allow remote posting." is confusing, because the normal feature is to post TO ping.fm and not FROM.
My suggestion would be:
- "Input your Ping.fm credentials below to enable posting to your social networking sites through ping.fm."
- show the "remote posting" hint only when the Ping.fm Node module is enabled.