added reference to risk calculation model
added reference to risk calculation model


Former-commit-id: 332ab5ebbee1521a7dcec08aadf03d3120a3d541 [formerly dcb45ede51f0e117c7d26633f01c5949b95daeff]
Former-commit-id: cfa9d802305dc7c2defef4fdf24307d066670da2
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine