[meta] use npmignore to autogenerate an npmignore file

.gitignore

@@ -17,3 +17,5 @@ Thumbs.db
 # Files that might appear on external disks
 .Spotlight-V100
 .Trashes
+
+.npmignore

package.json

@@ -30,6 +30,7 @@
 	},
 	"bugs": "https://github.com/mathiasbynens/String.fromCodePoint/issues",
 	"scripts": {
+		"prepack": "npmignore --auto --commentLines=autogenerated",
 		"lint": "eslint --ext=js,mjs .",
 		"postlint": "es-shim-api --bound",
 		"pretest": "npm run lint",
@@ -47,7 +48,13 @@
 		"@ljharb/eslint-config": "^21.0.1",
 		"eslint": "=8.8.0",
 		"functions-have-names": "^1.2.3",
+		"npmignore": "^0.3.0",
 		"nyc": "^10.3.2",
 		"tape": "^5.6.3"
+	},
+	"publishConfig": {
+		"ignore": [
+			".github/workflows"
+		]
 	}
 }