[meta] use npmignore to autogenerate an npmignore file

Author: ljharb

.gitignore

@@ -107,3 +107,5 @@ dist
 npm-shrinkwrap.json
 package-lock.json
 yarn.lock
+
+.npmignore

.npmignore

@@ -9,6 +9,7 @@
 		"./package.json": "./package.json"
 	},
 	"scripts": {
+		"prepack": "npmignore --auto --commentLines=autogenerated",
 		"prepublish": "not-in-publish || npm run prepublishOnly",
 		"prepublishOnly": "safe-publish-latest",
 		"lint": "eslint .",
@@ -49,6 +50,7 @@
 		"auto-changelog": "^2.4.0",
 		"eslint": "=8.8.0",
 		"mock-property": "^1.0.0",
+		"npmignore": "^0.3.0",
 		"nyc": "^10.3.2",
 		"safe-publish-latest": "^2.0.0",
 		"semver": "^6.3.0",
@@ -61,5 +63,10 @@
 		"commitLimit": false,
 		"backfillLimit": false,
 		"hideCredit": true
+	},
+	"publishConfig": {
+		"ignore": [
+			".github"
+		]
 	}
 }