feat: Add types

Author: rschristian

src/index.d.ts

@@ -43,11 +43,12 @@ type Options =
  *   shadow: true,
  *   mode: 'closed'
  * });
+ * const klass = register(PreactComponent, 'my-component');
  * ```
  */
 export default function register(
 	Component: AnyComponent,
 	tagName?: string,
 	propNames?: string[],
 	options?: Options
-): void;
+): HTMLElement;