Add instruction on navigating back to previous page

I have been searching in the tutorials and guides but unable to find the instruction on how to navigate back to the previous page. I hope this addition will help more users.

Author: stevenyap

docs/guides/NavigatingOutsideOfComponents.md

@@ -14,3 +14,9 @@ render(<Router history={browserHistory} routes={routes}/>, el)
 import { browserHistory } from 'react-router'
 browserHistory.push('/some/path')
 ```
+
+```js
+// Go back to previous page
+import { browserHistory } from 'react-router'
+browserHistory.goBack()
+```