logictree: added last bits of docs
logictree: added last bits of docs

Former-commit-id: 4e06fbf65ca183429262a2ebce7de46d04e0b496 [formerly dcb5d1a4fea52b0af754285ecb96971237dff026]
Former-commit-id: 29f225046e8282efab565ff98166c9d84c0deeca
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine