Added some info on the internals
Added some info on the internals


Former-commit-id: 71f0245c2e9cc90c972dd58dc67b1897dfe5fe63 [formerly 1e32dccb03d103c3c48af3fcef0ee3ca636cba71] [formerly 1e32dccb03d103c3c48af3fcef0ee3ca636cba71 [formerly 8be980e9dcebf7e816a815ecf11d7f0ebdf39611]]
Former-commit-id: a5e4bad4cd40c5f612361d3905500bc6624fa6e7
Former-commit-id: c1b7233813a84ee22d935c3781cc6f718843bf48
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine