Warn users to change password after account was created

app/views/notify/new_user_email.html.haml

@@ -12,5 +12,9 @@
   - unless Gitlab.config.gitlab.signup_enabled
     password..................................
     %code= @password
+
+%p
+  Please change your password immediatly after login.
+
 %p
   = link_to "Click here to login", root_url

app/views/notify/new_user_email.text.erb

@@ -7,4 +7,6 @@ login.................. <%= @user.email %>
   password............... <%= @password %>
 <% end %>
+Please change your password immediatly after login.
+
 Click here to login: <%= url_for(root_url) %>