[rules-users] Score traps - better docs

[Geoffrey De Smet]

Several users complained about not understanding "score traps", so for 
6.0 I 've improved the docs about it.
It also explains some way to deal with them.

https://github.com/droolsjbpm/drools-planner/blob/3f417ddeff270db83cc58b32a4150e99f4f8a378/drools-planner-docs/src/main/docbook/en-US/Chapter-Score_calculation/Chapter-Score_calculation.xml#L1088

HTH :)

PS: Wait for the 6.0 release if you want it in pretty format