Fix documented default value of index.threads

Change-Id: Id501ad3cd41848db3692ff0bc3b4935fd63d7e4f
diff --git a/Documentation/config-gerrit.txt b/Documentation/config-gerrit.txt
index fc08cdc..4881f2a 100644
--- a/Documentation/config-gerrit.txt
+++ b/Documentation/config-gerrit.txt
@@ -2400,9 +2400,10 @@
 
 [[index.threads]]index.threads::
 +
-Number of threads to use for indexing in normal interactive operations.
+Number of threads to use for indexing in normal interactive operations. If set
+to 0, indexing will be done in the same thread as the interactive operation.
 +
-Defaults to 1 if not set, or set to a negative value.
+Defaults to 0 if not set, or set to a negative value.
 
 [[index.batchThreads]]index.batchThreads::
 +