How about something like this as an intro:

> Sheperd is a graph based dependency resolution system, designed to simplify request pipelines that have multiple asynchronous steps. Sheperd makes it easy to split code in to fine-grained, composable units.

> For example, a feed may draw on multiple sources of data, all that need to be fetched in parallel, but that may have some common dependencies.... blah blah blah - fill out this example.

Then go into more technical detail.