Document a triaging workflow

We need to update this part of the documentation: https://freexian-team.pages.debian.net/debusine/reference/development-team-organization.html#project-management

We should also document a triaging workflow that helps support our objectives of triaging and responding to incoming issues within 7 days. I'm thinking of having an issue board showing issues that don't have the Backlogged label and that are in no milestone.