Added a warning on OQ_DISTRIBUTE=futures [skip CI]
Added a warning on OQ_DISTRIBUTE=futures [skip CI]


Former-commit-id: 2141eb1bb851b4ae32f3c348b90ee0f3ebc56190 [formerly fe148caf2e6cbf3b4e364533dc19ad955d7b772e]
Former-commit-id: f929c2e6200082de8abdc89fc7030b0ebcf782e6
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine