Change README to have quotes.

Author: kallentu

README.md

@@ -221,8 +221,8 @@ As an example, if we document the class Icon in flutter using the following:
 
 ```dart
 /// {@category Basics}
-/// {@category Assets, and Icons}
-/// {@subCategory Information displays}
+/// {@category "Assets and Icons"}
+/// {@subCategory "Information displays"}
 class Icon extends StatelessWidget {}
 ```
 
@@ -235,7 +235,7 @@ that will result in the following json:
     "href": "widgets/Icon-class.html",
     "type": "class",
     "categories": [
-      "Assets, Images, and Icons",
+      "Assets and Icons",
       "Basics"
     ],
     "subcategories": [