doc/git-howto: Replace "git push" example by one with dry-run

I do not think having "git push" as example is a good idea.
The command has a very high chance of pushing things which are unwanted to be
pushed
Reviewed-by: Carl Eugen Hoyos <cehoyos@ag.or.at>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

doc/git-howto.texi

@@ -326,10 +326,12 @@ faulty commit disappear from the history.
 @section Pushing changes to remote trees
 
 @example
-git push
+git push origin master --dry-run
 @end example
 
-Will push the changes to the default remote (@var{origin}).
+Will simulate a push of the local master branch to the default remote
+(@var{origin}). And list which branches and ranges or commits would have been
+pushed.
 Git will prevent you from pushing changes if the local and remote trees are
 out of sync. Refer to @ref{Updating the source tree to the latest revision}.