Add page on our "supporters" and donation infrastructure

[choldgraf]

In https://github.com/jupyterhub/team-compass/issues/508 we discussed a new supporters and donation infrastructure for mybinder.org. We should document these practices in the about section of our documentation, in order to make it explicit and to be transparent about these practices.

Since we've also discussed adding a list of sponsors/supporting institutions/etc to mybinder.org, I suggest that we leave that as the "source of truth" and in these docs we can just document the system itself and link to the home page for the official list.

[choldgraf]

Update: maybe supporters should be on docs.mybinder.org

The process of updating our banner on mybinder.org suggests to me that this is actually not the easiest place to keep regularly updated with new content, since we need to hard-code HTML when we update the mybinder.org home page.

Alternate proposal

How about instead of using mybinder.org as the source of truth for our "supporters" page, we instead use docs.mybinder.org for this. We could:

• Create a new page called Supporters of the Binder Project that lists team members, institutional partners, etc
• Create a YAML file that auto-populates that page with supporters of various kinds
• That YAML file is the source of truth, and we update it as our support network changes
• We could then programmatically generate the HTML needed on the mybinder.org page by pulling from that YAML file, and the source of truth would remain the same
• We could also update the banner on mybinder.org to be more "noticeable" and link to this "supporters of mybinder.org" page

[minrk]

Yeah, I think that's probably the best place to do it.