clarify relationship with theia-blueprint

[duncdrum]

While new issues keep appearing here, i have the impression that this repo has been superseded by the coder in theia-blueprint.

If that is the case, i would suggest to add prominent note to that effect on the readme.md and to then archive this repo. That way new users are stirred in the right direction, and feedback by early adopters can be collected in the new location under active maintenance.