Update install-cni-plugin.sh (#1792)

* Update install-cni-plugin.sh

* Update scripts/install-cni-plugin.sh

---------

Co-authored-by: Evan Baker <rbtr@users.noreply.github.com>

scripts/install-cni-plugin.sh

@@ -11,7 +11,8 @@ CNI_NETCONF_DIR=/etc/cni/net.d
 function usage
 {
     printf "Installs azure-vnet CNI plugins.\n"
-    printf "Usage: install-cni-plugin version [cniVersion]\n"
+    printf "See https://github.com/Azure/azure-container-networking/releases for versions\n"
+    printf "Usage: install-cni-plugin version [pluginVersion]\n"
 }
 
 if [ "$PLUGIN_VERSION" = "" ]; then