Clarify that you don't have to listen on HTTP
Clarify that you don't have to listen on HTTP

Per the following changes:

- chromium/hstspreload.appspot.com#47
- chromium/hstspreload@5c52e6516f3e2171bd6a75d641a2ddf099e36b35

It is no longer necessary to listen on HTTP *just* to serve a redirect to
HTTPS. Re-word the submission requirements to make this clear and match the
underlying library.

chromium/hstspreload.org,chromium/hstspreload.org,chromium/hstspreload.org,chromium/hstspreload.org