mention argument in extension test run() function (#214)

Fixes #213

Author: connor4312

lib/runTest.ts

@@ -73,6 +73,8 @@ export interface TestOptions {
 	 * When running the extension test, the Extension Development Host will call this function
 	 * that runs the test suite. This function should throws an error if any test fails.
 	 *
+	 * The first argument is the path to the file specified in `extensionTestsPath`.
+	 *
 	 */
 	extensionTestsPath: string;