Add description of importer plugin to the plugin documentation page

Change-Id: Iaac8a3dee82f5028afce8cf795376e56d57ce8d9
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>
diff --git a/Documentation/config-plugins.txt b/Documentation/config-plugins.txt
index fc42d36..bf21674 100644
--- a/Documentation/config-plugins.txt
+++ b/Documentation/config-plugins.txt
@@ -186,6 +186,7 @@
 link:https://gerrit-review.googlesource.com/#/admin/projects/plugins/codenvy[
 Project]
 
+[[delete-project]]
 === delete-project
 
 Provides the ability to delete a project.
@@ -249,6 +250,31 @@
 link:https://gerrit.googlesource.com/plugins/imagare/+doc/master/src/main/resources/Documentation/config.md[
 Configuration]
 
+=== importer
+
+The importer plugin allows to import projects from one Gerrit server
+into another Gerrit server.
+
+Projects can be imported while both source and target Gerrit server
+are online. There is no downtime required.
+
+The git repository and all changes of the project, including approvals
+and review comments, are imported. Historic timestamps are preserved.
+
+Project imports can be resumed. This means a project team can continue
+to work in the source system while the import to the target system is
+done. By resuming the import the project in the target system can be
+updated with the missing delta.
+
+The importer plugin can also be used to copy a project within one Gerrit
+server, and in combination with the link:#delete-project[delete-project]
+plugin it can be used to rename a project.
+
+link:https://gerrit-review.googlesource.com/#/admin/projects/plugins/importer[
+Project] |
+link:https://gerrit.googlesource.com/plugins/importer/+doc/master/src/main/resources/Documentation/about.md[
+Documentation]
+
 === Issue Tracker System Plugins
 
 Plugins to integrate with issue tracker systems (ITS), that (based