Get in touch with other a11y resources, link them and ask for back-linking

[jmuheim]

As discussed during the hackday 15. Lea will take care of this.

Todo:

• Search more resources (like Deque University, Powermapper, Axe, Google...)
• Link to them
  • Create separate page for this
  • Maybe give a brief summary on what they are specifically useful for, how they complement the ADG, etc.
• Ask them to link to us (netlinking?)

Resources (more to add):

• https://a11yproject.com/
  • Add our examples to the list of resources: https://a11yproject.com/resources/
• https://developer.mozilla.org/de/docs/Web/Barrierefreiheit
• Etc.