Document collections (sponsors, chapters)

[Tomasz-Kluczkowski]

What items are in, what data they hold, what images are used / required, where are they displayed, examples of usage.
We need to prepare this in such a way that a 5 year old can add a pull request with the necessary .md file to create a new sponsor or chapter. This should be exceptionally well done so that we can convince other groups to use this site for their events.