### templatetags/markdown.py

import markdown
import urllib2

from django import template
from django.template.defaultfilters import stringfilter
from django.utils.enconding import force_unicode
from django.utils.safestring import mark_safe

register = template.Library()

@register.filter(is_safe=True)
@stringfilter
def get_readme():
  extensions = []
  response = urllib2.urlopen('http://raw.github.com/shogun-toolbox/shogun/develop/README.md')
  readme = response.read()
  return mark_safe(markdown.markdown(force_unicode(readme), extensions, safe_mode=True,
                                     enable_attributes=False))

### templates/readme.html

{% extends "subpage.html" %}

{% block content %}
  <p>Test</p>
  {{ get_readme }}
{% endblock %}