Document stage 2

When a project passes stage 2 it requires to update few documents:

- https://github.com/OpenRailAssociation/technical-committee/blob/main/projects.md
- https://openrailassociation.org/#projects, currently we don't show the stage there, but if we want we need to add a custom field to the publiccode.yml
- Badge in project repository
- News entry on website 