add yarn watch command

package.json

@@ -8,7 +8,8 @@
   "scripts": {
     "compile": "concurrently \"yarn css\" \"yarn js\"",
     "css": "sass scss/:public/css --style=compressed --no-source-map",
-    "js": "tsc"
+    "js": "tsc",
+    "watch" : "concurrently \"tsc --watch\" \"sass --watch --style compressed scss/:public/css\" \"cd public && php -S locaLhost:1234\""
   },
   "devDependencies": {
     "@types/node": "^14.14.31",