Move contribution guide from the readme to CONTRIBUTING.md

With a link from the readme to the CONTRIBUTING.md.

The readme should be a presentation of the library and how to use it with linking the examples.

Then, comes the contribution.

changed milestone to %0.56.0

changed milestone to %0.57.0

changed title from Move contribution guide from the readme to a CONTRIBUTING.md to Move contribution guide from the readme to CONTRIBUTING.md

changed milestone to %1.0.0

added Easy pick label

changed milestone to %Backlog

changed milestone to %1.2.0

assigned to @moul

mentioned in commit 90b9f1d8

mentioned in merge request !188 (merged)

closed with merge request !188 (merged)