Improve docs about handling static files without django.contrib.staticfiles.

[loic84]

Following discussion on IRC with @apollo13 and @ubernostrum.

Since django.contrib.staticfiles is optional, we should document how to serve STATIC_URL without it during development; the docs for serving MEDIA_URL [ 1 ] may be used as a template.

Some parts of the docs need to be reviewed; for example "Note that the Django development server automatically serves the static files of the admin app (and any other installed apps)" [ 2 ] is actually only true if django.contrib.staticfiles is installed.

It might be helpful to warn that MEDIA_URL and STATIC_URL must have different values, the same applies to MEDIA_ROOT and STATIC_ROOT. This is mostly an issue because historically (pre-contrib.staticfiles) a lot of projects were using MEDIA_ROOT/MEDIA_URL to serve static files.

[ 1 ] ​https://docs.djangoproject.com/en/dev/howto/static-files/#serving-files-uploaded-by-a-user
[ 2 ] ​https://docs.djangoproject.com/en/dev/howto/deployment/wsgi/modwsgi/#serving-the-admin-files

[Tim Graham]

​PR

[Tim Graham <timograham@…>]

In 7b04038a7f4b291bc05124c4b5300001dc94e13f:

Fixed #20973 -- Document serving static files without django.contrib.staticfiles

[Tim Graham <timograham@…>]

In a62b640f7d3a0b90c4009cc7efe0a19fd3ad0bfa:

[1.6.x] Fixed #20973 -- Document serving static files without django.contrib.staticfiles

Backport of 7b04038a7f from master