DOC: add manual example for causal consistency (#368)
DOC: add manual example for causal consistency (#368)

* DOC: add manual example for causal consistency
ShaneHarvey/mongo-python-driver,mongodb/mongo-python-driver,ShaneHarvey/mongo-python-driver,ShaneHarvey/mongo-python-driver,mongodb/mongo-python-driver,mongodb/mongo-python-driver