Added Whats New for engine 3.8 [skip CI]
Added Whats New for engine 3.8 [skip CI]


Former-commit-id: 0d61706d85bf29a207f34732d91a8a3a7b3db0e9
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine