Add postCreateCommand in devcontainer

Author: adaex

.devcontainer.json

@@ -1,12 +1,8 @@
 // For format details, see https://aka.ms/devcontainer.json. For config options, see the README at:
 // https://github.com/microsoft/vscode-dev-containers/tree/main/containers/javascript-node
 {
-	"name": "coajs",
-	"image": "mcr.microsoft.com/vscode/devcontainers/javascript-node",
-	"extensions": [
-		"mutantdino.resourcemonitor",
-		"dbaeumer.vscode-eslint",
-		"esbenp.prettier-vscode",
-		"eamodio.gitlens",
-	],
+  "name": "coajs",
+  "image": "mcr.microsoft.com/vscode/devcontainers/javascript-node",
+  "postCreateCommand": "yarn",
+  "extensions": ["mutantdino.resourcemonitor", "esbenp.prettier-vscode", "dbaeumer.vscode-eslint", "eamodio.gitlens"]
 }