Add a comment for showing the Ruby backtrace outside a Ruby node when debugging

Author: eregon

src/main/java/org/truffleruby/language/backtrace/BacktraceFormatter.java

@@ -69,6 +69,8 @@ public static BacktraceFormatter createDefaultFormatter(RubyContext context) {
 
     // For debugging:
     // org.truffleruby.language.backtrace.BacktraceFormatter.printableRubyBacktrace(getContext(), this)
+    // When outside a Ruby node:
+    // org.truffleruby.language.backtrace.BacktraceFormatter.printableRubyBacktrace(RubyLanguage.getCurrentContext(), null)
     public static String printableRubyBacktrace(RubyContext context, Node node) {
         final BacktraceFormatter backtraceFormatter = new BacktraceFormatter(context, EnumSet.of(FormattingFlags.INCLUDE_CORE_FILES));
         final String backtrace = backtraceFormatter.formatBacktrace(null, context.getCallStack().getBacktrace(node));