Add “reading time” estimation to unread links

[rghedin]

Some “read it later” apps, such as Instapaper, shows an estimated reading time within each link saved. It's good to know beforehand how much time I'll need to spend reading a specific article.

Having something like this would be useful in Linkding, and the UI can accommodate this — adding the estimated reading time aside the “unread” tag, like Unread [9 min], for instance: