gerrit-config.txt: cache-automerge is for "merge" commmits

Change-Id: I952978259cf0507a200d5aa5246f1d3b1eb52bfd
diff --git a/Documentation/config-gerrit.txt b/Documentation/config-gerrit.txt
index cd15de7..5052386 100644
--- a/Documentation/config-gerrit.txt
+++ b/Documentation/config-gerrit.txt
@@ -1200,7 +1200,7 @@
 
 [[change.cacheAutomerge]]change.cacheAutomerge::
 +
-When reviewing diff commits, the left-hand side shows the output of the
+When reviewing merge commits, the left-hand side shows the output of the
 result of JGit's automatic merge algorithm. This option controls whether
 this output is cached in the change repository, or if only the diff is
 cached in the persistent `diff` cache.