build: add clean command to npm

package.json

@@ -9,7 +9,8 @@
     "parcel": "parcel",
     "dev": "concurrently --kill-others \"spago build --watch\" \"parcel watch src/background.js src/sidebar.js -d extension/\"",
     "build": "spago build && parcel build src/background.js src/sidebar.js -d extension/",
-    "test": "echo \"Error: no test specified\" && exit 1"
+    "test": "echo \"Error: no test specified\" && exit 1",
+    "clean": "rm -rf .cache .psci_modules modules dist extension/background.js extension/background.js.map extension/sidebar.js extension/sidebar.js.map"
   },
   "author": "",
   "license": "ISC",