Specify missing step

The instructions as given did not work. The reason they did not work was that, while my .bashrc was made aware of nvm, my running bash process did not know about nvm until I ran ". ~/bashrc", after which things worked as expected.

docs/GettingStarted.md

@@ -13,7 +13,7 @@ next: tutorial
 2. [Xcode](https://developer.apple.com/xcode/downloads/) 6.3 or higher is recommended.
 3. [Homebrew](http://brew.sh/) is the recommended way to install io.js, watchman, and flow.
 4. Install [io.js](https://iojs.org/) 1.0 or newer. io.js is the modern version of Node.
-  - Install **nvm** with [its setup instructions here](https://github.com/creationix/nvm#installation). Then run `nvm install iojs-v2 && nvm alias default iojs-v2`, which installs the latest compatible version of io.js and sets up your terminal so that typing `node` runs io.js. With nvm you can install multiple versions of Node and io.js and easily switch between them.
+  - Install **nvm** with [its setup instructions here](https://github.com/creationix/nvm#installation). To benefit from the changes to your .bashrc, run `source ~/.bashrc`. Then run `nvm install iojs-v2 && nvm alias default iojs-v2`, which installs the latest compatible version of io.js and sets up your terminal so that typing `node` runs io.js. With nvm you can install multiple versions of Node and io.js and easily switch between them.
   - New to [npm](https://docs.npmjs.com/)?
 5. `brew install watchman`. We recommend installing [watchman](https://facebook.github.io/watchman/docs/install.html), otherwise you might hit a node file watching bug.
 6. `brew install flow`. If you want to use [flow](http://www.flowtype.org).