Improve CT discoverability on mobile devices

[elylucas]

Comment from the docs rally:

On desktop, the left hand nav is very prominent and the "Component Testing" item is easy to find. On mobile, the main page does not discuss component testing until way down in the "Test types" section. The page linked in that section for "Component" no longer exists and gives a 404. The "Who uses Cypress?" section has a list of types of tests that Cypress enables and does not mention "Component".