add @blueprintjs/docs npm shield

README.md

@@ -21,6 +21,8 @@ This repository contains multiple projects in the `packages/` directory that are
 
 [![npm](https://img.shields.io/npm/v/@blueprintjs/core.svg?label=@blueprintjs/core)](https://www.npmjs.com/package/@blueprintjs/core) – Core styles & components.
 
+[![npm](https://img.shields.io/npm/v/@blueprintjs/docs.svg?label=@blueprintjs/docs)](https://www.npmjs.com/package/@blueprintjs/docs) – Documentation theme for [Documentalist](https://github.com/palantir/documentalist) data.
+
 [![npm](https://img.shields.io/npm/v/@blueprintjs/datetime.svg?label=@blueprintjs/datetime)](https://www.npmjs.com/package/@blueprintjs/datetime) – Components for interacting with dates and times.
 
 [![npm](https://img.shields.io/npm/v/@blueprintjs/table.svg?label=@blueprintjs/table)](https://www.npmjs.com/package/@blueprintjs/table) – Scalable interactive table component.