Improvements in HTML/Template chapters

[olasitarska]

A friend (Andrew Nesbitt) just went through our tutorial as a Python newbie and sent me his feedback. There are two things we can improve on, so I am just adding it here because I will forget it :)

1. When first adding the templates in http://tutorial.djangogirls.org/html/README.html I had to restart the server to get it to find the new templates, you mention about restarting the server in a later stage in the tutorial but not in that one.
2. I couldn't get http://tutorial.djangogirls.org/template_extending/README.html to work using just the content on the page, kept getting the TemplateDoesNotExists error, even after restarting, I ended up adding the following code to get it to work: https://github.com/andrew/django-girls-tutorial/blob/master/mysite/settings.py#L90-L92