fix: add include directory to package.json

Author: Amansingh0807

lib/node_modules/@stdlib/constants/float32/inv-two-pi/package.json

@@ -17,6 +17,7 @@
   "directories": {
     "doc": "./docs",
     "example": "./examples",
+    "include": "./include",
     "lib": "./lib",
     "test": "./test"
   },