Dash user-contributed docs

[auscompgeek]

Dash allows users to contribute docsets, as outlined in zealdocs/zeal#170. dasht should provide a command to automatically download and extract these as well.

(See also #4.)

[sunaku]

:+1: Thinking about how to implement this request has given way to a solution for other issues (#19, #15).

[dancju]

Scikit (sklearn) is an essential library in the machine learning industry. Its document is in the Dash-User-Contribution repo. I think Dash-User-Contributed documents is useful to machine learning users and many other users.

[d-miketa]

Hey, any update on this? It'd be super useful and https://github.com/zealdocs/zeal/issues/170#issuecomment-71310603 shows a way to get user-contributed docs.