improve RepositoryUpdate doc
improve RepositoryUpdate doc

  - make clear that there is only one RepositoryUpdate section

Change-Id: Ia2c2ea8d97f706c6318747745a327e4c07c9bbeb
Reviewed-by: Leena Miettinen <885fda02d52616fec24ed5fed9b3f0568fce3ead@digia.com>
Reviewed-by: Niels Weber <df24410c43e1f71d7f720aa26e4fcb77ce70f242@digia.com>

olear/qtifw,olear/qtifw,olear/qtifw,olear/qtifw