- Publish react-native.config.js (#25436)

Summary:
Looks we forgot to add this file to publish list. By adding it, we can remove some code in CLI that special-cases `react-native` package, since it now announces itself as a proper platform.

cc kelset, we'd like to have this cherry-picked for 0.60.

## Changelog

[Internal] [Fixed] - Publish `react-native.config.js`
Pull Request resolved: #25436

Test Plan: `npm pack` shows `react-native.config.js`

Differential Revision: D16071113

Pulled By: cpojer

fbshipit-source-id: df18affbb9a0ad7f2cfdd1a4cc93191aa5ffadeb

Author: thymikee

package.json

@@ -36,6 +36,7 @@
     "Libraries",
     "LICENSE",
     "packager",
+    "react-native.config.js",
     "react.gradle",
     "React.podspec",
     "React",