docs: add return value description to BrowserWindow#get(Content)Bounds (#19507)

docs/api/browser-window.md

@@ -913,7 +913,7 @@ console.log(win.getBounds())
 
 #### `win.getBounds()`
 
-Returns [`Rectangle`](structures/rectangle.md)
+Returns [`Rectangle`](structures/rectangle.md) - The `bounds` of the window as `Object`.
 
 #### `win.setContentBounds(bounds[, animate])`
 
@@ -925,7 +925,7 @@ the supplied bounds.
 
 #### `win.getContentBounds()`
 
-Returns [`Rectangle`](structures/rectangle.md)
+Returns [`Rectangle`](structures/rectangle.md) - The `bounds` of the window's client area as `Object`.
 
 #### `win.getNormalBounds()`