Add svg to the documentation of the --output arg of graph_models

[mardukbp]

In the current version of django-extensions (3.2.3) the documentation of the command graph_models

python manage.py graph_models --help

only mentions png and jpg as possible outputs. Searching in the GH issues I learned that svg is also supported. This should be included in the documentation. SVG is useful since it is not currently possible to specify the size or the dpi of the bitmap output (see #1429).

[varunsaral]

I think it will be easy to do. Just have to add the in svg in

django-extensions/django_extensions/management/commands/graph_models.py

Lines 95 to 99 in dd794f1

	'--output -o': {
	'action': 'store',
	'dest': 'outputfile',
	'help': 'Render output file. Type of output dependend on file extensions. Use png or jpg to render graph to image.',
	},