Added some notes about the datastore [skip CI]
Added some notes about the datastore [skip CI]


Former-commit-id: c4562b23a0ddddbe4cb007ae93caab12143963b3 [formerly edee285488159b94a04d3d4ce41d3b64003bdadd]
Former-commit-id: aba1eddfa4448e59d0968923746b69c629e325dc
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine