[RFC] Add ScrollView bounded height explanation

Summary:
As discussed in our internal group, think this is a fairly easy error to run into so I added some explanation.

@frantic / @vjeux open to better wording here, but I tried to explain how setting the height directly is discouraged and it's probably better to pipe `flex: 1` all the way down.

I didn't regenerate the website since the script assumes some permissions (push permission to master repo) and has some missing npm dependencies (and after fixing that, still had some obscure error :P )
Closes https://github.com/facebook/react-native/pull/1633
Github Author: Peter Cottle <pcottle@fb.com>

Test Plan: Imported from GitHub, without a `Test Plan:` line.

Libraries/Components/ScrollView/ScrollView.js

@@ -42,6 +42,14 @@ var INNERVIEW = 'InnerScrollView';
  * Component that wraps platform ScrollView while providing
  * integration with touch locking "responder" system.
  *
+ * Keep in mind that ScrollViews must have a bounded height in order to work,
+ * since they contain unbounded-height children into a bounded container (via
+ * a scroll interaction). In order to bound the height of a ScrollView, either
+ * set the height of the view directly (discouraged) or make sure all parent
+ * views have bounded height. Forgetting to transfer `{flex: 1}` down the
+ * view stack can lead to errors here, which the element inspector makes
+ * easy to debug.
+ *
  * Doesn't yet support other contained responders from blocking this scroll
  * view from becoming the responder.
  */