Adds validation check for "React" package name

- "React" is a reserve word and cannot be used as a project name since it will break the Sample app when generated

react-native-cli/index.js

@@ -65,6 +65,15 @@ function validatePackageName(name) {
     );
     process.exit(1);
   }
+
+  if (name === 'React') {
+    console.error(
+      '"%s" is not a valid name for a project. Please do not use the reserve ' +
+        'word "React".',
+      name
+    );
+    process.exit(1);
+  }
 }
 
 function init(name) {