Apply sandbox badge (#210)
Apply sandbox badge (#210)

This PR applies sandbox badge to the repository to signal
the level of maturity of the project as agreed by Eiffel
Bootstrap Technical Committee.

See https://github.com/eiffel-community/community/blob/master/PROJECT_LIFECYCLE.md#project-lifecycle-stages
for the details of project lifecycle.

See https://hackmd.io/SCImga0nS1qSh3QvsEOAVQ?view for the
discussion that took place during past Eiffel Bootstrap
Technical Committee Meetings.
Ericsson/eiffel-remrem-publish,Ericsson/eiffel-remrem-produce