Add sageDB and Modify README

[PiotrNewt]

1. Modification SageDB introduces machine learning methods to modify the data structures, algorithms and load balancing model involved in optimizing the database.

2. Suggestion The combination of database and machine learning has a lot of research results, and I think it is possible to open a new section ( Database + Machine learning ) for placing these excellent papers instead of putting them in "Trends".

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If author agrees, I am happy to modify and improve this repository in this regard.