Documentation: Add new page, Image Library, as child of Using Backdrop

[izmeez]

It may be helpful for new users and others to learn about the image library. How to access it and what it can do.

Searching the documentation fails to find an existing page on the "Image library".

Even though image library is in core, there is no default admin bar menu item to content image library. Finding it can be a bit challenging.

[stpaultim]

Yes, the image library seems to be just an option for uploading images on some fields. It's not a thing on it's own. You can go to the image library directly. Maybe you should be able to.

Some documentation could be useful. It could also be used better in core.

• Views: Provide a new "File browser" display type, and make it available when creating views of type "Files" (part of a bigger plan) backdrop/backdrop-issues#6512
• [META][UX] Improvements for the image library backdrop/backdrop-issues#1307