Activating Open Collective

[xdamman]

This pull request adds backers and sponsors from your Open Collective https://opencollective.com/research-engine ❤️

It adds two badges at the top to show the latest number of backers and sponsors. It also adds placeholders so that the avatar/logo of new backers/sponsors can automatically be shown without having to update your README.md. [more info]

See how it looks on this repo.

We have also added a postinstall script to let people know after npm|yarn install that you are welcoming donations. [More info]

[blackforestboi]

@xdamman Thanks for adding this PR. Very excited to be part of open collective.

Looking forward to foster the open-source ecosystem!