@anyone (cc @ilyakava & @AshFurrow): Shortten posts by adding <!--more--> tags

Currently on [our blog's front-page](http://artsy.github.io/) we have a couple posts fully laid out taking up most of the page real-estate. This uses the `<!-- more -->` tag to cut off the post at a point I thought was appropriate for a teaser. I'm not slapping any hands here—this is easy to miss because... Jeckyll ¯\\_(ツ)_/¯