[meta] use npmignore to autogenerate an npmignore file

Author: ljharb

.gitignore

@@ -9,3 +9,5 @@ package-lock.json
 # coverage data
 coverage/
 .nyc_output/
+
+.npmignore

.npmignore

@@ -59,11 +59,13 @@
         "falafel": "^2.2.4",
         "js-yaml": "^3.14.0",
         "npm-run-posix-or-windows": "^2.0.2",
+        "npmignore": "^0.3.0",
         "safe-publish-latest": "^2.0.0",
         "tap": "^8.0.1",
         "tap-parser": "^3.0.5"
     },
     "scripts": {
+        "prepack": "npmignore --auto --commentLines=autogenerated",
         "prepublishOnly": "safe-publish-latest",
         "prepublish": "!(type not-in-publish) || not-in-publish || npm run prepublishOnly",
         "prelint:files": "git ls-files 2>/dev/null | xargs find 2> /dev/null | grep -vE 'node_modules|\\.git' || echo '*.md *.js test/*.js'",
@@ -106,5 +108,10 @@
         "email": "mail@substack.net",
         "url": "http://substack.net"
     },
-    "license": "MIT"
+    "license": "MIT",
+    "publishConfig": {
+        "ignore": [
+            ".github/workflows"
+        ]
+    }
 }