docs: fix typed typo typing the wrong type

Author: keithamus

README.md

@@ -227,7 +227,7 @@ declare global {
   interface HTMLElement {
     addEventListener<K extends keyof CustomEventMap>(
       type: K,
-      listener: (this: Document, ev: CustomEvent<CustomEventMap[K]>) => unknown,
+      listener: (this: HTMLElement, ev: CustomEvent<CustomEventMap[K]>) => unknown,
       options?: boolean | AddEventListenerOptions
     ): void
   }