add Hello Web App to books section

README.md

@@ -126,6 +126,7 @@
 ## Books
 
 * [Django for Beginners: Learn web development with Django 2.0](https://leanpub.com/djangoforbeginners)
+* [Hello Web App 2.0](https://hellowebbooks.com/learn-django/)
 * [Two Scoops of Django: Best Practices for Django 1.11](https://www.twoscoopspress.com/products/two-scoops-of-django-1-11/)
 * [Build Your First Website with Python and Django 1.11](https://www.amazon.com/Build-First-Website-Python-Django/dp/0994616856)
 * [Test-Driven Development with Python](https://www.amazon.com/dp/1491958707)