Update building instructions

Author: gaearon

content/docs/how-to-contribute.md

@@ -130,19 +130,27 @@ First, run `yarn build`. This will produce pre-built bundles in `build` folder,
 
 The easiest way to try your changes is to run `yarn build react/index,react-dom/index --type=UMD` and then open `fixtures/packaging/babel-standalone/dev.html`. This file already uses `react.development.js` from the `build` folder so it will pick up your changes.
 
-If you want to try your changes in your existing React project, you may copy `build/dist/react.development.js`, `build/dist/react-dom.development.js`, or any other build products into your app and use them instead of the stable version. If your project uses React from npm, you may delete `react` and `react-dom` in its dependencies and use `yarn link` to point them to your local `build` folder:
+If you want to try your changes in your existing React project, you may copy `build/dist/react.development.js`, `build/dist/react-dom.development.js`, or any other build products into your app and use them instead of the stable version. 
+
+If your project uses React from npm, you may delete `react` and `react-dom` in its dependencies and use `yarn link` to point them to your local `build` folder. Note that **instead of `--type=UMD` you'll want to pass `--type=NODE` when building**. You'll also need to build the `scheduler` package:
 
 ```sh
-cd ~/path_to_your_react_clone/build/node_modules/react
+cd ~/path_to_your_react_clone/
+yarn build react/index,react-dom/index,scheduler --type=NODE
+
+cd build/node_modules/react
 yarn link
-cd ~/path_to_your_react_clone/build/node_modules/react-dom
+cd build/node_modules/react-dom
 yarn link
-cd /path/to/your/project
+
+cd ~/path/to/your/project
 yarn link react react-dom
 ```
 
 Every time you run `yarn build` in the React folder, the updated versions will appear in your project's `node_modules`. You can then rebuild your project to try your changes.
 
+If some package is still missing (e.g. maybe you use `react-dom/server` in your project), you can always do a full build with `yarn build`. Note that running `yarn build` without options takes a long time.
+
 We still require that your pull request contains unit tests for any new functionality. This way we can ensure that we don't break your code in the future.
 
 ### Style Guide {#style-guide}