Use same title as in router

I think that saying "Clone from another Tails" here was on purpose,
taking for granted that people would already know what "clone" means in
this context. But let's try the other way first...

wiki/src/upgrade/clone.mdwn

 [[!meta robots="noindex"]]
-[[!meta title="Clone from another Tails"]]
+[[!meta title="Upgrade from another Tails"]]
 [[!meta stylesheet="install/inc/stylesheets/steps" rel="stylesheet" title=""]]
 [[!meta stylesheet="install/inc/stylesheets/upgrade-clone" rel="stylesheet" title=""]]