Update README.md

Author: TheMuellenator

README.md

@@ -125,6 +125,11 @@
 ## 11. Am I Rich? (a.k.a. Bitcoin Ticker)
 
 * [Bitcoin Ticker Stub Project](https://github.com/londonappbrewery/bitcoin-ticker-flutter)
+* [Flutter DropdownButton](https://docs.flutter.io/flutter/material/DropdownButton-class.html)
+* [Dropdown Menu Design](https://material.io/design/components/menus.html#dropdown-menu)
+* [99 Bottles of Beer Programming Language Collection](http://www.99-bottles-of-beer.net/)
+* [DartPad For in Loop Mini Challenge](https://dartpad.dartlang.org/88fd2dd04c921892515bcd0567ef1636)
+* [Bitcoin Average API Docs](https://apiv2.bitcoinaverage.com/)
 * [Bronze Challenge Start Code](https://github.com/londonappbrewery/bitcoin-flutter-challenge-start)
 * [Silver Challenge Starter Code](https://github.com/londonappbrewery/bitcoin-flutter-silver-start)
 * [Gold Challenge Starter Code](https://github.com/londonappbrewery/bitcoin-flutter-gold-start)