Mention the possibility of resetting the password for new accounts (#3812)

This solves the problem of administrators creating accounts for users
that then do not know their initial password (without the administrator
sending it to them via some other channel).

templates/mail/auth/register_notify.tmpl

@@ -9,6 +9,7 @@
 	<p>Hi <b>{{.Username}}</b>, this is your registration confirmation email for {{AppName}}!</p>
 	<p>You can now login via username: {{.Username}}.</p>
 	<p><a href="{{AppUrl}}user/login">{{AppUrl}}user/login</a></p>
+	<p>If this account has been created for you, please <a href="{{AppUrl}}user/forgot_password">reset your password</a> first.</p>
 	<p>© <a target="_blank" rel="noopener" href="{{AppUrl}}">{{AppName}}</a></p>
 </body>
 </html>