(bug 42253) link user in accountcreatedtext msg

Why not provide links to new user's page and talk page?  This is only
when a logged-in user creates a new account, so presumably he or she
knows what he's doing and appreciates the convenience links.

Also improve documentation of accountcreated in MessagesQqq.php.

Change-Id: I4e88829d8665c5c61a59877962a8a14b55c91aa0
Merge "(bug 42253) link user in accountcreatedtext msg"