Add getting started to contributing.md (redfin#349)

CONTRIBUTING.md

@@ -14,6 +14,61 @@ You could:
 
 Not sure where to start? Join us [on gitter](https://gitter.im/redfin/react-server) and ask!
 
+## Getting started
+
+React Server uses a tool called [lerna](https://www.npmjs.com/package/lerna) to
+manage the entire React Server ecosystem in a single repository.  This allows
+maintainers to know that everything works together well, without having to know
+all of the inner workings of each package in the monorepo.  It does present some
+challenges to new developers, since the idea is relatively new.  If you want to
+know more about why we chose a monorepo, check out the [babel monorepo design
+doc](https://github.com/babel/babel/blob/master/doc/design/monorepo.md),
+especially the [previous discussion](https://github.com/babel/babel/blob/master/doc/design/monorepo.md#previous-discussion).
+
+To get your local clone into working order, run an
+
+```
+npm run bootstrap
+```
+
+If things get hairy and you have errors that you don't understand, you can get
+a clean install of all the dependencies
+
+```
+npm run nuke
+npm run bootstrap
+```
+
+If you've been running `bootstrap` to track down build errors a lot, and have a
+lot of debug files lying around, you can clean them up
+
+```
+npm run clean
+```
+
+Most commands have a corresponding `lerna` command; if you want to find out more,
+you can look at the `scripts` hash in the root `package.json`, check out the
+[lerna docs](lernajs.io), and run the lerna commands yourself
+
+```
+npm i -g lerna david
+lerna clean
+lerna bootstrap
+lerna run lint
+lerna exec -- david u
+```
+
+You can also work on a single package by `cd`-ing into that module, and using
+normal `npm` scripts
+
+```
+cd packages/generator-react-server
+npm i
+npm test
+```
+
+but you should still run a full monorepo build and test before submitting a pr.
+
 ## Testing
 
 Yeah!  Do it!