docs: Provide content for bluejay-docs user guides

[motero2k]

Update according to the new tpa-designer flow:

• [ ] Add new courses
• [ ] Create a tpa template for a course
• [ ] Automate computations for a course
• [ ] Register new teams (update if necessary)
• [ ] Update registered teams
• [x] Register Slack hooks

[motero2k]

TODO: check what fields can be changed when updating the info.yml. If name changes, it is considered a new team and not an update.