document changes in api contract

docs/api/breaking-changes.md

@@ -8,6 +8,29 @@ The `FIXME` string is used in code comments to denote things that should be fixe
 
 # Planned Breaking API Changes (5.0)
 
+## `app.getFileIcon(path[, options], callback)`
+
+The `getFileIcon` function on `app` taking a callback is being deprecated in favor of a version returning a Promise.
+
+```js
+const path = 'some/path/to/your/icon'
+// Deprecated
+app.getFileIcon(path, (err, icon) => {
+  if (err) {
+    console.log('oh no an error!', err)
+  } else {
+    console.log(icon)
+  }
+})
+// Replace With
+app.getFileIcon(path)
+  .then(icon => {
+    console.log(icon)
+  }).catch(err => {
+    console.log('oh no an error!', err)
+  })
+```
+
 ## `new BrowserWindow({ webPreferences })`
 
 The following `webPreferences` option default values are deprecated in favor of the new defaults listed below.