Add 'Update Mechanism: Manual' to README.chromium files

Bug: 445311061
Change-Id: I2b756ad5795b793be54855c8e1883a2a2d8bbefd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6953660
Reviewed-by: Jiewei Qian <[email protected]>
Auto-Submit: Jordan Brown <[email protected]>
Reviewed-by: Rachael Newitt <[email protected]>
Commit-Queue: Jordan Brown <[email protected]>
Owners-Override: Jordan Brown <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1516347}
NOKEYCHECK=True
GitOrigin-RevId: 305b2fe1fa7a2c66e0ffee71ff6cdab160c570a8
diff --git a/README.chromium b/README.chromium
index 7752bc1..c6e8443 100644
--- a/README.chromium
+++ b/README.chromium
@@ -1,6 +1,7 @@
 Name: jsoncpp
 URL: https://github.com/open-source-parsers/jsoncpp
 Version: 1.9.4
+Update Mechanism: Manual
 CPEPrefix: cpe:/a:jsoncpp_project:jsoncpp:1.9.4
 License: JsonCPP
 License File: LICENSE