Add license information for the media content

[carolinan]

Add information about license and source for the media content. This was recently requested in the #themereview WordPress Slack channel and is needed when theme authors intend to use the images in screenshots etc.

If information can not be found consider replacing the images.

[TeBenachi]

How about something like this? The info are from the handbook. https://make.wordpress.org/themes/handbook/review/resources/#licenses-bundled-resources

======== Title Screenshot: Image license attributions

All the images in the screenshot must be under a 100% GPL or compatible license. The following licenses are suitable for the themes in the directory.

CC0 CC BY 4.0 CC-BY-SA 4.0 – Compatible with the GPLv3 only.

Recommended websites (for images):

Pexels - Note pexels has two different licenses, CCO and "Legal Simplicity" license. CCO License are allowed. "Legal Simplicity" are NOT allowed.

stocksnap.io skitterphoto.com mystock.photos pickupimage.com pxhere.com foodiesfeed.com Smithsonian Open Access

Restricted websites:

The following websites are NOT allowed. Consider using different images.

unsplash.com freeimages.com scx.hu photopin.com splitshire.com pixabay.com freepik.com flaticon.com pikwizard.com adobe stock envato elements undraw.co