Clarify new installation vs. upgrade of plugin in 2.9 release notes

The download-commands plugin can be either newly installed, or
upgraded, when installing Gerrit 2.9

Make this a bit clearer in the release notes.

Change-Id: If6feeb5122d8bdc4272d086f540485dc66a0e44d
diff --git a/ReleaseNotes/ReleaseNotes-2.9.txt b/ReleaseNotes/ReleaseNotes-2.9.txt
index 9f2c920..ff307b2 100644
--- a/ReleaseNotes/ReleaseNotes-2.9.txt
+++ b/ReleaseNotes/ReleaseNotes-2.9.txt
@@ -37,10 +37,11 @@
 `download-commands` core plugin or any other plugin providing download
 commands is installed. The `download-commands` plugin provides the
 standard download schemes and commands. It is packaged together with
-Gerrit and can be installed during the
+Gerrit and can be installed, or upgraded, during the
 site initialization]:
+.Installing the plugin for the first time
 - Batch init:
 By default the batch init does *not* install any core plugin. To
@@ -60,7 +61,8 @@
   Install plugin download-commands version v2.9 [y/N]? y
-Pay attention that the 2.8 version of the `download-commands` plugin is
+.Upgrading the plugin
+Pay attention that the `download-commands` plugin from Gerrit 2.8 is
 *not* compatible with Gerrit 2.9 and must be upgraded:
 - Batch init: