[meta] use npmignore to autogenerate an npmignore file

Author: ljharb

Diff for: .gitignore

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

Diff for: .npmignore

@@ -12,6 +12,7 @@
 		"./package.json": "./package.json"
 	},
 	"scripts": {
+		"prepack": "npmignore --auto --commentLines=autogenerated",
 		"prepublish": "not-in-publish || npm run prepublishOnly",
 		"prepublishOnly": "safe-publish-latest",
 		"preversion": "auto-changelog",
@@ -59,6 +60,7 @@
 		"evalmd": "^0.0.19",
 		"functions-have-names": "^1.2.2",
 		"has-strict-mode": "^1.0.1",
+		"npmignore": "^0.3.0",
 		"nyc": "^10.3.2",
 		"safe-publish-latest": "^2.0.0",
 		"tape": "^5.5.3"
@@ -77,5 +79,10 @@
 		"commitLimit": false,
 		"backfillLimit": false,
 		"hideCredit": true
+	},
+	"publishConfig": {
+		"ignore": [
+			".github/workflows"
+		]
 	}
 }