added pm2 configuration file

ecosystem.config.js

@@ -0,0 +1,21 @@
+const os = require("os");
+const env = require("dotenv").config();
+
+const cores = os.cpus().length;
+
+module.exports = {
+  apps: [
+    {
+      name: "mailman",
+      script: "build/main.js",
+      env: env.parsed,
+      watch: ["build", "client/build"],
+      ignore_watch: ["node_modules"],
+      watch_options: {
+        followSymlinks: false
+      },
+      instances: cores,
+      exec_mode: "cluster"
+    }
+  ]
+};