Doc: use standard wording in \brief commands

QDoc does some magic with the \class and \namespaces
and \brief commands, so the following wording must be used:
"The xxx class yyy ..."

Change-Id: Id231f30e8464898b776888d5423523de404aae34
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/plugins/vcsbase/checkoutprogresswizardpage.cpp

@@ -38,8 +38,10 @@
 /*!
     \class VcsBase::CheckoutProgressWizardPage
 
-    \brief Page showing the progress of an initial project checkout. Turns complete when the job
-           succeeds.
+    \brief The CheckoutProgressWizardPage implements a page showing the
+    progress of an initial project checkout.
+
+    Turns complete when the job succeeds.
 
     \sa VcsBase::BaseCheckoutWizard
 */