Update default config in docs to match code

[hugovk]

To match:

sphinx-notfound-page/notfound/extension.py

Lines 280 to 283 in fd6e9b9

	default_context = {
	'title': 'Page not found',
	'body': "<h1>Page not found</h1>\n\nUnfortunately we couldn't find the content you were looking for.",
	}

[humitos]

Thanks!