adding a recommended extension of prettier

.vscode/extensions.json

@@ -0,0 +1,8 @@
+{
+  // See http://go.microsoft.com/fwlink/?LinkId=827846
+  // for the documentation about the extensions.json format
+  "recommendations": [
+    // Extension identifier format: ${publisher}.${name}. Example: vscode.csharp
+    "esbenp.prettier-vscode"
+  ]
+}