Adding --autocomplete flag to 5.0 release notes

[llvmbot]

Bugzilla Link	34155
Resolution	FIXED
Resolved on	Aug 11, 2017 09:19
Version	5.0
OS	All
Blocks	#33196
Reporter	LLVM Bugzilla Contributor
CC	@zmodem

Extended Description

We've added --autocomplete flag to clang, but forgot to write this information to release notes.

Fixed in: https://reviews.llvm.org/rL310700

[zmodem]

Merged in r310723.