[meta] use npmignore to autogenerate an npmignore file

Author: ljharb

.gitignore

@@ -8,3 +8,5 @@ npm-debug.log
 npm-shrinkwrap.json
 package-lock.json
 yarn.lock
+
+.npmignore

.npmignore

@@ -4,6 +4,7 @@
   "description": "AST utility module for statically analyzing JSX",
   "main": "lib/index.js",
   "scripts": {
+    "prepack": "npmignore --auto --commentLines=autogenerated",
     "prebuild": "rimraf lib",
     "build": "babel src --out-dir lib",
     "prepublishOnly": "safe-publish-latest && npm test && npm run build",
@@ -36,6 +37,7 @@
     "in-publish": "^2.0.1",
     "jest": "^20.0.4",
     "jest-cli": "^20.0.4",
+    "npmignore": "^0.3.0",
     "object.entries": "^1.1.5",
     "object.fromentries": "^2.0.5",
     "rimraf": "^2.7.1",
@@ -71,5 +73,10 @@
   "dependencies": {
     "array-includes": "^3.1.5",
     "object.assign": "^4.1.2"
+  },
+  "publishConfig": {
+    "ignore": [
+      ".github/workflows"
+    ]
   }
 }