daemon: Fix --site-path documentation

We failed to document --site-path.

Change-Id: I519589027e14a9223ccd0ff5929c272f25323c08
Signed-off-by: Shawn O. Pearce <sop@google.com>

Documentation/pgm-daemon.txt

@@ -8,7 +8,8 @@ daemon - Gerrit network server
 SYNOPSIS
 --------
 [verse]
-'java' -DGerritServer=PATH -jar gerrit.war 'daemon'
+'java' -jar gerrit.war 'daemon'
+	-d <SITE_PATH>
 	[\--enable-httpd | \--disable-httpd]
 	[\--enable-sshd | \--disable-sshd]
 	[\--console-log]
@@ -29,6 +30,11 @@ to different values.
 OPTIONS
 -------
 
+-d::
+\--site-path::
+	Location of the gerrit.config file, and all other per-site
+	configuration data, supporting libaries and log files.
+
 \--enable-httpd::
 \--disable-httpd::
 	Enable (or disable) the internal HTTP daemon, answering