modules/users: warn when fallback groups is used

- Warn here since it may not be what the Distributor want.
  Having wrong groups may result in broken permissions for
  created user.
- explain what defaultGroups is for in users.conf

src/modules/users/UsersViewStep.cpp

@@ -2,6 +2,7 @@
  *
  *   Copyright 2014-2015, Teo Mrnjavac <teo@kde.org>
  *   Copyright 2017, Adriaan de Groot <groot@kde.org>
+ *   Copyright 2017, Gabriel Craciunescu <crazy@frugalware.org>
  *
  *   Calamares is free software: you can redistribute it and/or modify
  *   it under the terms of the GNU General Public License as published by
@@ -131,6 +132,7 @@ UsersViewStep::setConfigurationMap( const QVariantMap& configurationMap )
     }
     else
     {
+        cDebug() << "WARNING: Using fallback groups. Please check defaultGroups in users.conf";
         m_defaultGroups = QStringList{ "lp", "video", "network", "storage", "wheel", "audio" };
     }
 

src/modules/users/users.conf

@@ -11,6 +11,8 @@
 # These globalconfig keys are set when the jobs for this module
 # are created.
 ---
+# Used as default groups for the created user.
+# Adjust to your Distribution defaults.
 defaultGroups:
     - users
     - lp
@@ -19,6 +21,7 @@ defaultGroups:
     - storage
     - wheel
     - audio
+
 autologinGroup:  autologin
 doAutologin:     true