Update sponsors component

[maxrjones]

I started the sponsors component with NASA and NSF because I know they've funded large components of the work. We should update this component to align with the tiers in https://github.com/pangeo-data/governance/blob/main/sponsorship.md#sponsorship-tiers and add missing sponsors.

Past page content: https://github.com/pangeo-data/pangeo/blob/master/docs/collaborators.rst