Update(package.json): Adding new search keywords

Add more keywords for the package like theme and css theme.

re #53

Author: markusguenther

Diff for: package.json

@@ -13,6 +13,9 @@
     "url": "https://github.com/FriendsOfReactJS/react-css-themr/issues"
   },
   "keywords": [
+    "theme",
+    "css theme",
+    "react css theme",
     "css-modules",
     "customization",
     "react",