Alerts: BIP148: mention backups

_alerts/2017-07-12-disruptive-forks.md

@@ -48,11 +48,12 @@ pending payments to confirm on the Bitcoin block chain before the event.
 1. If you send bitcoins as payments, note that many services may stop
 accepting bitcoins at {{start}} or earlier.
 
-1. Be wary of storing your bitcoins on an exchange or other third-party
-wallet.  If they accept transactions during the event, they could lose
-money and will likely spread those loses across all their users.  If
-there end up being two or more competing versions of Bitcoin, then they
-may refuse to give you your bitcoins on versions they don't like.
+1. Be wary of storing your bitcoins on an exchange or any service that
+doesn't allow you to make a local backup copy of your private keys.  If
+they accept transactions during the event, they could lose money and
+will likely spread those loses across all their users.  If there end up
+being two or more competing versions of Bitcoin, then they may refuse to
+give you your bitcoins on versions they don't like.
 
 ## During the event