Add reactjs#111 manually.

Author: timdorr

lessons/11-productionish-server/README.md

@@ -58,8 +58,10 @@ app.listen(PORT, function() {
 
 Now run:
 
-```
+```sh
 NODE_ENV=production npm start
+# For Windows users:
+# SET NODE_ENV=production npm start
 ```
 
 Congratulations! You now have a production server for this app. After