Updated to include TEMPLATE requirement for Django 1.9+

In Django 1.9+ if you do not add: 'builtins': ['overextends.templatetags.overextends_tags'], to your TEMPLATES section you will receive a TemplateSyntaxError when the overextends template files are rendered: "Invalid block tag on line".  Including 'builtins': ['overextends.templatetags.overextends_tags'], per the overextends docs (and experience) resolves this error.

https://github.com/stephenmcd/django-overextends

docs/advanced_topics/customisation/branding.rst

@@ -19,6 +19,18 @@ Install ``django-overextends`` with ``pip install django-overextends`` (or add `
       # ...
     )
 
+    # For Django 1.9+ you must also add overextends to the builtins key of your TEMPLATES setting:
+    TEMPLATES = [
+        {
+            'BACKEND': 'django.template.backends.django.DjangoTemplates',
+            'APP_DIRS': True,
+            'OPTIONS': {
+                # ...
+                'builtins': ['overextends.templatetags.overextends_tags'],
+            }
+        },
+    ]
+
 The template blocks that are available to be overridden are as follows:
 
 ``branding_logo``