CHANGELOG.md: Add entry for v0.16.0
CHANGELOG.md: Add entry for v0.16.0

coreos/prometheus-operator,brancz/prometheus-operator,gianrubio/prometheus-operator,brancz/prometheus-operator,jescarri/prometheus-operator,coreos/prometheus-operator,jescarri/prometheus-operator,gianrubio/prometheus-operator,gianrubio/prometheus-operator,brancz/prometheus-operator