LSC Add 'Update Mechanism:' to README.chromium

Bug: 417367156
Change-Id: I318629733d1f75262e030105ec0b684f1307d2fd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6646426
Auto-Submit: Jordan Brown <rop@google.com>
Owners-Override: Jordan Brown <rop@google.com>
Commit-Queue: Jordan Brown <rop@google.com>
Commit-Queue: Jiewei Qian <qjw@chromium.org>
Reviewed-by: Jiewei Qian <qjw@chromium.org>
Reviewed-by: Rachael Newitt <renewitt@google.com>
Reviewed-by: Joey Scarr <jsca@google.com>
Cr-Commit-Position: refs/heads/main@{#1475401}
NOKEYCHECK=True
GitOrigin-RevId: da752eb2a3660cf1bf8dac620f6380b89dd953a7

README.chromium

diff --git a/README.chromium b/README.chromium
index c275dd3..50f78e0 100644
--- a/README.chromium
+++ b/README.chromium
@@ -2,6 +2,7 @@
 URL: https://github.com/google/brotli
 Version: 9801a2c5d6c67c467ffad676ac301379bb877fc3
 Revision: 9801a2c5d6c67c467ffad676ac301379bb877fc3
+Update Mechanism: Manual
 License: MIT
 License File: LICENSE
 Security Critical: yes