Fix document for get mergeable information for change

If the flag for other-branches is set, we will only check for branches
that are listed branchOrder section in project config.

Change-Id: Ifa2977deea0444ae597e391bbb1453bb3b6d48a6
diff --git a/Documentation/rest-api-changes.txt b/Documentation/rest-api-changes.txt
index 7724ceb..11b2729 100644
--- a/Documentation/rest-api-changes.txt
+++ b/Documentation/rest-api-changes.txt
@@ -3565,7 +3565,9 @@
 ----
 
 If the `other-branches` parameter is specified, the mergeability will also be
-checked for all other branches.
+checked for all other branches which are listed in the
+link:config-project-config.html#branchOrder-section[branchOrder] section in the
+project.config file.
 
 .Request
 ----