Give storybook feature parity with the registry

[wheresrhys]

Just been doing a compare and contrast of various locations of documentation. 3 main things missing:

• SassDoc: I would guess it's possible to plug something in to (or perhaps before?) the storybook build that pumps the sassdoc out into each component's root so that it appears in storybook.
• The info and helpful links section
  : shoudl similarly be possible to autogenerate a .md file in each component's root
• Version selector - no idea how to replace this, but it does feel like a need that needs to be thought about if the direction of travel is towards storybook being the primary demo mechanism