examples - add missing setup.sh for mattermost

examples/mattermost/setup.sh

@@ -0,0 +1,11 @@
+#!/bin/bash
+
+if [ $(id -u) -ne 0 ] ; then
+	echo "❌ Run me as root"
+	exit 1
+fi
+
+if [ ! -d ./volumes/app/mattermost ] ; then
+	mkdir -p ./volumes/app/mattermost/{config,data,logs,plugins,client/plugins,bleve-indexes}
+fi
+chown -R 2000:2000 ./volumes/app/mattermost