Add comment about collectArguments() on when it's used

Author: eregon

src/launcher/java/org/truffleruby/launcher/RubyLauncher.java

@@ -132,6 +132,11 @@ protected void launch(Context.Builder contextBuilder) {
         System.exit(exitValue);
     }
 
+    /**
+     * This is only used to provide suggestions when an option is misspelled.
+     * It should only list options which are parsed directly by the CommandLineParser.
+     * Normal SDK options are already handled by the common Launcher code.
+     */
     @Override
     protected void collectArguments(Set<String> options) {
         options.addAll(Arrays.asList(