Update shell openExternal docs (from review)

diff --git a/docs/api/shell.md b/docs/api/shell.md
index d96df89..bfe2ae0 100644 (file)
--- a/docs/api/shell.md
+++ b/docs/api/shell.md
@@ -40,9 +40,11 @@ Open the given file in the desktop's default manner.
 * `options` Object (optional) _macOS_
   * `activate` Boolean - `true` to bring the opened application to the
     foreground. The default is `true`.
-* `callback` Function (optional) _macOS_
+* `callback` Function (optional) - If specified will perform the open asynchronously. _macOS_
+  * `opened` Boolean
 
 Returns `Boolean` - Whether an application was available to open the URL.
+If callback is specified, it will return whether it was able to initiate the open call.
 
 Open the given external protocol URL in the desktop's default manner. (For
 example, mailto: URLs in the user's default mail agent).