[added] lerna to README

Reviewers: markwei, O2 Material Motion

Reviewed By: markwei, O2 Material Motion

Subscribers: markwei

Tags: #material_motion

Differential Revision: http://codereview.cc/D1926

README.md

@@ -1,22 +1,30 @@
 # Material Motion for JavaScript #
 
-This is an experimental implementation of the concepts outlined in the [Material
-Motion Starmap](https://material-motion.gitbooks.io/material-motion-starmap/content/).
+This repo houses the JavaScript implementation of Material Motion.  For more information about the project as a whole, check [the Starmap](https://material-motion.github.io/material-motion/starmap/).
 
-### High-level Goals ###
+## High-level Goals ##
 
-- To enable the motions and gestures [proposed in the Material
-  Spec](https://material.google.com/motion/material-motion.html) to be easily
-  implemented by application authors in the JS ecosystem.
+- To enable the motions and gestures [described in the Material Spec](https://material.google.com/motion/material-motion.html) to be easily implemented by application authors in the JS ecosystem.
 
 - To make prototyping new animated experiences simpler.
 
-- To allow authors to write views in terms of URLs, and have the system guide
-  the transitions between them.
+- To allow authors to write views in terms of URLs, and have the system guide the transitions between them.
 
-- To yield a system that feels robust by default.  Fragile transitions erode
-  user trust in the overall system: “should I enter my password in a glitchy
-  app?”
+- To yield a system that feels robust by default.  Fragile transitions erode user trust in the overall system: “should I enter my password in a glitchy app?”
+
+## Organization ##
+
+This repo houses all the packages that comprise the Material Motion implementation for JavaScript.  They are available in [`packages`](https://github.com/material-motion/material-motion-js/tree/develop/packages/):
+
+- [`runtime`](https://github.com/material-motion/material-motion-experiments-js/tree/develop/packages/runtime/) houses the [Runtime](https://material-motion.github.io/material-motion/starmap/specifications/runtime/Runtime/).  It provides a centralized place for all motion to be registered, so work can be coordinated appropriately and displayed in tooling.
+
+## Contributing ##
+
+We use [lerna](https://lernajs.io/) to make it easier to work across packages.  Rather than running [`yarn`](https://yarnpkg.com/) (or `npm`) in the individual package folders, just use `lerna` from the root:
+
+- `lerna bootstrap` will install each packages dependencies, linking across between appropriately when they depend on one another.  This is similar to running `yarn install` in each package.
+
+- `lerna run test` will run the tests specified in each package's `package.json` file.
 
 ## License ##