Add content for react fundamentals

content/roadmaps/103-react/content/100-react-fundamental-topics/readme.md

@@ -1 +1,7 @@
-# React fundamental topics
+# React
+
+React is a JavaScript library for building user interfaces. It is an open-source, component-based front end library responsible only for the view layer of the application.
+
+<ResourceGroupTitle>Free Content</ResourceGroupTitle>
+<BadgeLink colorScheme='blue' badgeText='Official Website' href='https://reactjs.org/'>Official Website</BadgeLink>
+<BadgeLink colorScheme='blue' badgeText='Official Docs' href='https://reactjs.org/docs/getting-started.html'>Official Documentation</BadgeLink>