Add contributions

[fbastian]

We should add a "contribution" section to the README. It is even more important since we have killed all the git history when making the source code public, thus deleting all contributors.

@marcrr: I know you have a detailed log of all contributions, maybe you could share it here so that I format the information in the README?

[marcrr]

see suggested co-authors on p. 2 of https://docs.google.com/document/d/1Zh9brOIOdagau7-PNRt5B2EWg_hOUqIiwgO_MAVLogw/edit