Add docs badge.

Author: idlesign

src/makeapp/app_templates/__default__/README.md

@@ -4,6 +4,9 @@
 
 [![PyPI - Version](https://img.shields.io/pypi/v/{{ app_name }})](https://pypi.python.org/pypi/{{ app_name }})
 [![License](https://img.shields.io/pypi/l/{{ app_name }})](https://pypi.python.org/pypi/{{ app_name }})
+[![Docs](https://img.shields.io/readthedocs/{{ app_name }})](https://{{ app_name }}.readthedocs.io/)
+{% block badges %}
+{% endblock %}
 
 **Work in progress. Stay tuned.**