contributing: Clarify the behavior for multiple CLs submission

Change-Id: I2eb651480193a1d9044829b721625a1abc145b1f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/docs/+/3626582
Auto-Submit: Yiwei Zhang <yiwzhang@google.com>
Commit-Queue: Yiwei Zhang <yiwzhang@google.com>
Tested-by: Yiwei Zhang <yiwzhang@google.com>
Reviewed-by: Jonathan Fan <jonfan@chromium.org>
diff --git a/contributing.md b/contributing.md
index b7fb07f..1710ea5 100644
--- a/contributing.md
+++ b/contributing.md
@@ -257,8 +257,8 @@
 ### CL dependencies {#CQ-DEPEND}
 
 Sometimes work will span multiple [CL]s across different repos. The `Cq-Depend:`
-lines are used to make sure [CL]s are merged in a specific order, or altogether
-vs none at all.
+lines are used to make sure [CL]s are merged in a specific order and [CQ]
+attempt to merge [CL]s altogether.
 
 *   Specify dependencies in the last paragraph of your change, just before
     `Change-Id:`, using `Cq-Depend: chromium:12345`.
@@ -276,10 +276,10 @@
     `chrome-internal:4321`).
 *   You may specify `Cq-Depend` loops where "CL A" depends on "CL B", and "CL B"
     depends on "CL A" (there's no limit to the number of [CL]s). This makes sure
-    the [CQ] will pick up and test them together atomically.
-*   Atomic transactions within a single repository are supported.
-    *   Merges across repos is not atomic due to [Gerrit] limitations. There is
-        a small window where syncs may pull a partial set of changes.
+    the [CQ] will pick up and test them together.
+*   Atomic submission/merge is not guaranteed but best-effort supported by [CQ]
+    due to [Gerrit] limitations.
+    *   There is a small window where syncs may pull a partial set of changes.
 
 Here's an example: