TBR: lib: Prepare all repos for open-sourcing.
TBR: lib: Prepare all repos for open-sourcing.

The CONTRIBUTING file is added to all repos, and also added
to the jiri-copyright tool so that repos can be automatically
checked and fixed.

I've run jiri copyright fix against all repos to fix up
outstanding issues.

MultiPart: 5/23

Change-Id: I9bab542ff1bfcf8c634f645bfa79680d78d76b2d

vanadium/go.lib