Add guide to visualisation from metrics

[mwalzer]

which values are in the metrics, best practices, code examples

[mwalzer]

e.g. to value distribution terms, how to use the quantiles

[mwalzer]

maybe general guide to metric terms with two sections:

1. visualisation
2. use/interpretation
3. combination (mapping rules)
   For 2. when 'it depends...' e.g. the peak density indications for issues in different modes/scenarios: peakpick algo; fragmentation scheduling or ion collection; sample content, local reference/consistency; additional identification assessment

[mwalzer]

For 3. default interpretations in case mapping term is missing? (Any relationship: has_value_concept STATO:0000036 ! outlier term should have a threshold definition term)

[bittremieux]

Rather than in the specification document, this can be part of the online documentation. This is more related to specific examples and providing guidance, rather than the technical specification.

[bittremieux]

#266 will address visualization to some extent. More context/metric-dependent visualizations are best left to specialized tools, e.g. pMultiQC has several visualizations.

Metrics use/interpretation will be addressed by the quality interpretation type dimension proposed in #323. More detailed metric interpretation information should be specified using the comment: field in the CV for each specific metric, rather than too high-level general instructions.