update install flow

[aarondruck]

after the user installs the add on from here: https://togetherjs.com/hotdish/

it should go to this page:

data/site-pages/02-first-run.html

[ianb]

@gregglind : I'm not sure how I should detect addon installation. Using a flag in simplestorage that we check when main.js is loaded would be the easiest way, but seems crude.