add notes

README.md

 
 - Support of special components like Video / GL views remains untested.
 - It's preferable to **use a background color on the view you rasterize** to avoid transparent pixels and potential weirdness that some border appear around texts.
-- on Android, you need to make sure `collapsable` is set to `false` if you want to snapshot a **View**. Otherwise that view won't reflect any UI View. ([found by @gaguirre](https://github.com/gre/react-native-view-shot/issues/7#issuecomment-245302844))
-- if you want to share out the screenshoted file on Android, you will have to copy it somewhere first so it's accessible to an Intent, see comment: https://github.com/gre/react-native-view-shot/issues/11#issuecomment-251080804 .
+
+### Notes specific to Android implementation
+
+- you need to make sure `collapsable` is set to `false` if you want to snapshot a **View**. Otherwise that view won't reflect any UI View. ([found by @gaguirre](https://github.com/gre/react-native-view-shot/issues/7#issuecomment-245302844))
+- if you want to share out the screenshoted file, you will have to copy it somewhere first so it's accessible to an Intent, see comment: https://github.com/gre/react-native-view-shot/issues/11#issuecomment-251080804 .
+-  if you implement a third party library and want to get back a File, you must first resolve the `Uri`. the `file` result returns an `Uri` so it's consistent with iOS and you can give it to `Image.getSize` for instance.
 
 ## Getting started