Make screenshots accessible

[hexabinaer]

Don't know if there might be constraints ... but shouldn't images be accessible for screenreaders?

Thinking along those lines:

[lang]:
  screenshots:
    - url: ...
      alt: "Description of what's visible in screenshot"
    - url: ...
      alt: ...

Nice to have (really nice): Attribution

[lang]:
  screenshots:
    - url: ...
      alt: "Description of what's visible in screenshot"
      attributionUrl: https://creativecommons.org/licenses/by-sa/4.0/
      attributionName: "Awesome Creator"
    - url: ...
      alt: ...

[bfabio]

@hexabinaer I like the idea. Maybe attributionUrl and attributionName are pushing it, because they would describe an external resource, which we never do elsewhere in the publiccode.yml spec.

WDYT?