Enhance Stage 2 documentation with Aggregate label/key
In https://www.ow2.org/view/MRL/Stage2-ProjectAttributes#HComputation, Bug Handling
is the Aggregate's human readable name for act_bugs
system label which is currently displayed in the dendrogram.
A first step in regard with #97 is to add a mention to the label name for all Aggregates we have listed in the documentation.