feat(docs): Add some basic API documents.

@zaach, @6a68, @nchapman - could I get a review of these? I'm adding @6a68 and @nchapman because they need some docs NOW.
This link 404ed for me, but I'm never sure if things need to be merged before they resolve correctly. GitHub is tricky w/ links sometimes.

Also, not sure if you want to remove `grunt ` prefix from each of the task names to prevent line breaks. Or not, whatever.