[meta] use npmignore to autogenerate an npmignore file

.gitignore

@@ -9,3 +9,5 @@ yarn.lock
 
 # symlinked file used in tests
 test/resolver/symlinked/_/node_modules/package
+
+.npmignore

package.json

@@ -17,6 +17,7 @@
 		"module"
 	],
 	"scripts": {
+		"prepack": "npmignore --auto --commentLines=autogenerated",
 		"prepublishOnly": "safe-publish-latest && cp node_modules/is-core-module/core.json ./lib/ ||:",
 		"prepublish": "not-in-publish || npm run prepublishOnly",
 		"prelint": "eclint check $(git ls-files | xargs find 2> /dev/null | grep -vE 'node_modules|\\.git')",
@@ -38,6 +39,7 @@
 		"in-publish": "^2.0.1",
 		"mkdirp": "^0.5.5",
 		"mv": "^2.1.1",
+		"npmignore": "^0.3.0",
 		"object-keys": "^1.1.1",
 		"rimraf": "^2.7.1",
 		"safe-publish-latest": "^2.0.0",
@@ -58,5 +60,11 @@
 		"is-core-module": "^2.9.0",
 		"path-parse": "^1.0.7",
 		"supports-preserve-symlinks-flag": "^1.0.0"
+	},
+	"publishConfig": {
+		"ignore": [
+			".github/workflows",
+			"appveyor.yml"
+		]
 	}
 }