[FEAT] Demo time/frequency monitoring: add more explanations

[tbouffard]

Is your feature request related to a problem? Please describe. To make it clearer we could add

• [x] legends about the overlay colors (#208)
• [x] The display of the legends could also be conditional to the choice: no black legend for overlays, no color legend for paths. #234
• [x] Meaning of the color/thickness code for overlays In the legend, the two color blocks (green/red) should come with a label (activities, transitions (or paths)). See #233 Green and red have meanings of "Good, Right, Ok" for green and "Bad, Wrong, Error" for red. Plus, color blind people may have a hard time making the difference. Another pair of colors would be better. #236
• [ ] legends about what the path stroke width means
• [ ] more explanations in the description
• [ ] explain we use simulated data. We can add a link to https://process-analytics.github.io/bpmn-visualization-js/#process_data
• [x] others to be checked: see https://github.com/process-analytics/bpmn-visualization-examples/pull/221#issuecomment-912117093

[csouchet]

See Nathalie's comment: https://github.com/process-analytics/bpmn-visualization-examples/pull/221#issuecomment-912117093