[Bash-autocompletion] Add comment to test so that it is easier to fix

Summary:
clang/test/Driver/autocomplete.c is a test for --autocomplete, and this
test might break if people add/modify flags or HelpText. So I've add
comment for future developers so that they can fix this file according
to the change they had made.

Reviewers: v.g.vassilev, teemperor, ruiu

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D36209

llvm-svn: 309794

clang/test/Driver/autocomplete.c

@@ -1,3 +1,7 @@
+// Test for the --autocompletion flag, which is an API used for shell
+// autocompletion. You may have to update tests in this file when you
+// add/modify flags, change HelpTexts or the values of some flags.
+
 // RUN: %clang --autocomplete=-fsyn | FileCheck %s -check-prefix=FSYN
 // FSYN: -fsyntax-only
 // RUN: %clang --autocomplete=-std= | FileCheck %s -check-prefix=STD