[JS] Create Documentation

[asfimport]

https://github.com/apache/arrow/tree/master/js currently only has a handful of examples but no API documentation.

Reporter: Dominik Moritz / @domoritz

_{Note: This issue was originally created as ARROW-2688. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
There is published auto-generated API documentation: http://arrow.apache.org/docs/js/. It would be useful to start a user-facing prose documentation project (like the non-API parts of http://arrow.apache.org/docs/python/), is that what you mean?

It would be good to point users to the API documentation in the JS readme. I opened ARROW-2697 about this

[asfimport]

Dominik Moritz / @domoritz:
I think arrow js needs both user-facing prose documentation and API docs with comments for each component.