Use container.replica as the property for readonly replicas

Change-Id: Ifd2f55107425bc6a1f9202d676694ba9c07d93c4
diff --git a/Documentation/config-gerrit.txt b/Documentation/config-gerrit.txt
index 00350d1..982d7c6 100644
--- a/Documentation/config-gerrit.txt
+++ b/Documentation/config-gerrit.txt
@@ -1565,12 +1565,16 @@
 Execute `java -jar gerrit.war daemon --help` to see all possible
 options.
 
-[[container.slave]]container.slave::
+[[container.replica]]container.replica::
 +
 Used on Gerrit replica installations. If set to true the Gerrit JVM is
 called with the '--replica' switch, enabling replica mode. If no value is
 set (or any other value), Gerrit defaults to master mode.
 
+[[container.replica]]container.slave::
++
+Backward compatibility for 'container.slave' config setting.
+
 [[container.startupTimeout]]container.startupTimeout::
 +
 The maximum time (in seconds) to wait for a gerrit.sh start command