Added the client, server & dev script to the package.json

package.json

@@ -5,7 +5,16 @@
   "repository": "https://github.com/gnmyt/PowerTools.git",
   "author": "Mathias Wagner <germannewsmaker@gmail.com>",
   "license": "MIT",
+  "scripts": {
+    "client": "cd client && yarn start",
+    "server": "nodemon server.js",
+    "dev": "concurrently --kill-others-on-fail \"yarn server\" \"yarn client\""
+  },
   "dependencies": {
     "express": "^4.18.2"
+  },
+  "devDependencies": {
+    "concurrently": "^8.0.1",
+    "nodemon": "^2.0.22"
   }
 }