Correct example of export command usage in documentation

The documentation was showing the old style command invocation
from when the review notes export was done with a server program.

Change the example to show usage via the plugin's ssh command.

Change-Id: Iecdb73d9e6b331960a5c9ae8017a22694e912e11

src/main/resources/Documentation/cmd-export.md

diff --git a/src/main/resources/Documentation/cmd-export.md b/src/main/resources/Documentation/cmd-export.md
index 0c06c7e..7f4351d 100644
--- a/src/main/resources/Documentation/cmd-export.md
+++ b/src/main/resources/Documentation/cmd-export.md
@@ -43,5 +43,5 @@
 To generate all review information:
 
 ```
-  $ java -jar gerrit.war ExportReviewNotes -d site_path --threads 16
+  $ ssh -p 29418 user@review reviewnotes export --threads 16
 ```