update css static file code example

Example 1: django cannot update static css

<link rel='stylesheet' type='text/css' href="{% static 'css/yourname.css' %}?20181209">

Example 2: django static files

{% load static %}
<img src="{% static "my_app/example.jpg" %}" alt="My image">

Example 3: django static files

STATICFILES_DIRS = [
    os.path.join(BASE_DIR, "static"),
    '/var/www/static/',
]