Improve docstrings for language types

Author: henrymercer

lib/languages.js

@@ -1,11 +1,12 @@
+/** A language supported by CodeQL. */
+export type Language = string;
+
 /**
- * A CodeQL language.
+ * A language supported by CodeQL that is treated specially by the Action.
  *
- * To facilitate adding new languages, this is a typedef rather than an
- * exhaustive list of languages supported by CodeQL.
+ * This is not an exhaustive list of languages supported by CodeQL and new
+ * languages do not need to be added here.
  */
-export type Language = string;
-
 export enum KnownLanguage {
   csharp = "csharp",
   cpp = "cpp",