docs: correct key code reqs for accel doc (#14825)

docs/api/accelerator.md

@@ -2,7 +2,7 @@
 
 > Define keyboard shortcuts.
 
-Accelerators are Strings that can contain multiple modifiers and key codes,
+Accelerators are Strings that can contain multiple modifiers and a single key code,
 combined by the `+` character, and are used to define keyboard shortcuts
 throughout your application.