Onboarding page requirements

[GaurangTandon]

Here is everything we must display in the welcome page. We wish to keep it short and sweet and to the point, so only cover essential items.

Cover interactively:

1. basic snippet expansion, with rich text support, using hotkey
2. context menu insertion
3. placeholders and tab key shifting
4. auto inserts (also show how we can disable them, this has been a popular concern among uninstall feedback)

Cover with less detail:

1. Omnibox suport
2. Blocking sites
3. Contacting us for help when needed