Use templates for issues and pull requests

Created by: nounoursheureux

It encourages contributors to describe and explain the changes they made/the issue they encounter. My pull requests for example tend to be quite vague because we already discuss on Mattermost, and that makes it hard to follow for someone who wasn't part of the discussion. If the issue doesn't fit the template really well you can still choose to ignore it. The Redox kernel is already using them, so we may as well use the same templates to have a unified experience for contributors of the Redox project: redox-os/redox#567 Tell me what you think about it !