feat: update package.json to include gypfile and additional directories

Author: sethdivyansh

lib/node_modules/@stdlib/stats/base/dists/normal/mean/package.json

@@ -14,11 +14,14 @@
     }
   ],
   "main": "./lib",
+  "gypfile": true,
   "directories": {
     "benchmark": "./benchmark",
     "doc": "./docs",
     "example": "./examples",
+    "include": "./include",
     "lib": "./lib",
+    "src": "./src",
     "test": "./test"
   },
   "types": "./docs/types",