XSS filtering has recently been added to `swh-web` (D1322) for the rendering
of README files in markdown format.
But as @kalpitk noticed it, the rendering of images located in an origin source tree
is now broken.
So instead of using `showdown-xss-filter` package, prefer to use the `dompurify`
one which seems to have a good default white list for XSS filtering.
Related T1642