"Learn about Iodide Premium" button, landing page, survey

@hamilton @teonbrooks @mdboom @wlach

To help us get a sense of interest in "premium features", we should add a button to Iodide something along the lines of "Learn about Iodide Premium" (or similar) to the iodide landing page (at least).

We should follow standard practices WRT this kind of thing -- the button should be in a prominent location and in a high contrast/visibility color etc.

here's a draft blurb, please add your thoughts:
https://docs.google.com/document/d/12c64uVRFcrhd8ABOvM3JW5kTTMGp1TSHk1bLFU_8S6U/edit

we'll also need to do a little survey. i'll talk to mozilla's survey folks for help with that