[repo.xml]: Missing documentation on storing files as binary

[joewiz]

Describe the problem

The article at https://exist-db.org/exist/apps/doc/repo does not account for the feature added by @JoernT in eXist-db/exist#727. That PR added support for a <resources> element in repo.xml, which enables storing HTML files as binary to avoid eXist's assumption that .html files are XML. This element is not described in the section on repo.xml, i.e., https://exist-db.org/exist/apps/doc/repo#sect-repoxml.

Please provide the following

• exist-db version: 6.1.0
• documentation version: 6.1.0