docs: Document the display object

Fix #3571.

docs/api/screen.md

@@ -54,6 +54,23 @@ app.on('ready', function() {
 });
 ```
 
+## The `Display` object
+
+The `Display` object represents a physical display connected to the system. A
+fake `Display` may exist on a headless system, or a `Display` may correspond to
+a remote, virtual display.
+
+* `display` object
+  * `id` Integer - Unique identifier associated with the display.
+  * `rotation` Integer - Can be 0, 1, 2, 3, each represents screen rotation in
+    clock-wise degrees of 0, 90, 180, 270.
+  * `scaleFactor` Number - Output device's pixel scale factor.
+  * `touchSupport` String - Can be `available`, `unavailable`, `unknown`.
+  * `bounds` Object
+  * `size` Object
+  * `workArea` Object
+  * `workAreaSize` Object
+
 ## Events
 
 The `screen` module emits the following events: