Updated TextInput prop doc

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I am a web developer, who recently started coding for mobile apps using react-native. I was trying to use the `inlineImageLeft` props of TextInput, but I found that it's docs weren't sufficient. So a PR for it.

No code change. Updated the docs under website folder. Screenshot for the change below.

![screen shot 2017-08-30 at 4 39 32 pm](https://user-images.githubusercontent.com/6011865/29869747-e73d9dde-8da1-11e7-912a-16e3115b8296.png)
Closes #15708

Differential Revision: D5738795

Pulled By: hramos

fbshipit-source-id: b8b6cbac5c50abd4d8a6ef8089dc9d92bc0b7f6f

Libraries/Components/TextInput/TextInput.js

@@ -513,6 +513,13 @@ const TextInput = createReactClass({
 
  /**
  * If defined, the provided image resource will be rendered on the left.
+ * The image resource must be inside `/android/app/src/main/res/drawable` and referenced
+ * like
+ * ```
+ * <TextInput
+ * inlineImageLeft='search_icon'
+ * />
+ * ```
  * @platform android
  */
  inlineImageLeft: PropTypes.string,