Make the main documentation title less Geocities

This is probably the lamest patch ever, but then again "Welcome to The
Linux Kernel's documentation" is nearly equally lame. Really, we don't
need to "Welcome" people to the documentation, just tell them what the
site is about.

Signed-off-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>