container.slave defaults to --slave behavior

When running Gerrit in large environments it's sometimes necessary
to configure Gerrit slave installations.  This change adds the
configuration option container.slave, if set to true gerrit.sh
is called with the slave switch. If no value is set (or any other
value), Gerrit defaults to master mode.

Change-Id: Ic4103e0d3d952e0d56b6aa5101d20c960588772a
diff --git a/Documentation/config-gerrit.txt b/Documentation/config-gerrit.txt
index b455c92..ccaabc7 100644
--- a/Documentation/config-gerrit.txt
+++ b/Documentation/config-gerrit.txt
@@ -512,6 +512,12 @@
 values are configured, they are passed in order on the command line,
 separated by spaces.  These options are appended onto 'JAVA_OPTIONS'.
 
+[[container.slave]]container.slave::
++
+Used on Gerrit slave installations. If set to true the Gerrit JVM is
+called with the '--slave' switch, enabling slave mode. If no value is
+set (or any other value), gerrit defaults to master mode.
+
 [[container.user]]container.user::
 +
 Login name (or UID) of the operating system user the Gerrit JVM