Typo correction for d-i i18n and l10n Guide

[Tapio Lehtonen <tale@iki.fi>]

*** level3.xml-original	2005-12-30 22:12:10.743999776 +0200
--- level3.xml	2005-12-30 22:12:55.274494125 +0200
***************
*** 12,18 ****
  
  <para>
  The level 3 of translations groups together the components of the
! installation process which are not always been used. These steps are
  optional steps and do no occur on default installs.
  </para>
  
--- 12,18 ----
  
  <para>
  The level 3 of translations groups together the components of the
! installation process which are not always used. These steps are
  optional steps and do no occur on default installs.
  </para>