Document the chosen user scenarios #6

Document the user scenarios of the marketing documents in docs/marketing under one name: "chosen user scenarios". A chosen user scenario is a question that a developer asks about an existing codebase or about a code change, and that Heidrun Data answers with evidence.

The seven chosen user scenarios

1. Explain a technical decision. The developer asks: "Why did we choose this technology or design?" Source: four_scenarios_existing_code.md.
2. Find previous attempts. The developer asks: "What have we already tried to solve this problem?" Source: four_scenarios_existing_code.md.
3. Reconstruct a module's history. The developer asks: "Tell me the history of this module and what I should know before changing it." Source: four_scenarios_existing_code.md.
4. Estimate the impact of a change. The developer asks: "If I change this function, what could be affected?" Source: four_scenarios_existing_code.md.
5. Optimize a slow function with evidence. The developer asks: "Can this part of the software be made faster while keeping its behavior?" This scenario needs Code Spine to run the software. Source: active_code_analysis_and_optimization.md.
6. Keep the reason behind a design decision after a developer leaves. The question is the same as in scenario 1, and the answer comes from the shared data of a team. Source: heidrun_data_team.md.
7. Remember an optimization attempt. The question is the same as in scenario 2 and scenario 5, and the answer comes from the shared experiment records of a team. Source: heidrun_data_team.md.

Scenarios 1 to 4 use only historical project records and static code analysis. They do not need to run the software. Scenarios 5 and 7 need the experiment records of Code Spine. Scenarios 6 and 7 need Heidrun Data Team, which is a proposal.

The first two scenarios to demonstrate

Scenario 1 and scenario 3 are the first two to demonstrate, on the repository Heidrun Notebook, with the workspace heidrun_data_example_database of the folder testbed_folder/. The work of scenario 3 is in issue 7.

Done when

• The documentation of the repository lists the seven chosen user scenarios with the name "chosen user scenarios".
• Each chosen user scenario has its question, the records that answer it, the shape of the answer, and its limits.

Related: issue 169 in heidrun_notebook