Update index.html

Fixed two words inversions.
Merge pull request #65 from AurelioDeRosa/patch-1

Fix typo (is method => method is).
Update index.html

Fixed two words inversions.
Added note: non-visible docs get stalled orientation (closes #28)
Tried to fix queuing problem (closes #47, #30)
Fixes based on Mounir's suggestions
Merge pull request #64 from w3c/page_visibility

Page visibility