Add MobX State manager README

Author: Seth Lemmons

24-mobx-state/README.md

@@ -0,0 +1,15 @@
+# 24 Handling Application State with MobX
+
+This subdirectory contains an app already generated with create-react-app, as
+described in the "Handling Application State with MobX"  blog post (link here)
+
+To run the app server:
+
+```
+$ cd a-application-state-redux
+$ npm install
+$ npm start
+```
+
+A browser window will automatically open and will load the app.
+