docs: add gluon-luci-wifi-config to the example site.mk

docs/site-example/site.mk

@@ -20,6 +20,7 @@ GLUON_SITE_PACKAGES := \
 	gluon-luci-admin \
 	gluon-luci-autoupdater \
 	gluon-luci-portconfig \
+	gluon-luci-wifi-config \
 	gluon-next-node \
 	gluon-mesh-vpn-fastd \
 	gluon-radvd \